在紧张局势持续数周后，美国官员警告称，俄罗斯可能会对乌克兰发动攻击”随时。"

美国官员称，俄罗斯花了数周时间在乌克兰东部附近集结军事力量，逾15万军队在白俄罗斯和边境的俄罗斯一侧包围了乌克兰。

克里姆林宫否认即将入侵的警告，并在最近几天声称正在撤出部分部队，而美国和北约官员表示，商业卫星图像显示，没有降级的迹象。

随着全球领导人继续进行外交努力，以避免俄罗斯和乌克兰之间的战争，美国国务院一名高级官员周四告诉美国广播公司新闻，这是“自冷战结束以来，和平与安全最危险的时刻。”

随着这场冲突在全球舞台上演，美国人有点混杂美国应该如何应对。在一个昆尼皮亚克大学的新民意调查，57%的美国人表示，如果俄罗斯入侵，美国不应派兵进入乌克兰，54%的人支持拜登部署军队支持北约盟友的决定。

Jim Lo Scalzo/EPA via Shutterstock

乔·拜登总统就俄罗斯在乌克兰边境的军事集结对媒体发表讲话.

本周早些时候，乔·拜登总统向美国公众发表讲话并再次明确表示美国不会派兵支持乌克兰。但他承诺捍卫北约的“每一寸土地”，已经向欧洲增派了数千名士兵，并承诺用致命的防御性武器、经济援助以及美国及其盟国对俄罗斯的严厉制裁来支持乌克兰人民及其政府。

他说，美国的高级别参与是必要的，因为“这不仅仅是俄罗斯和乌克兰的事情。”

“这是为了坚持我们的信念，为了我们世界的未来，为了自由，为了无数国家选择自己命运的权利。以及人民决定自己未来的权利，或者一个国家不能用武力改变邻国边界的原则，”拜登说。“如果我们不在自由今天受到威胁的地方坚持自由，我们明天肯定会付出更大的代价。”

北约关系

奥古斯塔大学(Augusta University)政治学副教授、情报和安全研究主任克雷格·艾伯特(Craig Albert)告诉美国广播公司新闻(ABC News)，要了解美国在这场冲突中的既得利益，你必须回到冷战时期。

为了对抗苏联在欧洲的侵略，美国在1949年帮助成立了北约安全联盟，即北大西洋公约组织。自那以后，北约已经扩张了几次，包括增加了三个前苏联加盟共和国。

东邻俄罗斯的前苏联加盟共和国乌克兰不是北约成员国，尽管该联盟在2008年向其敞开了大门。俄罗斯总统弗拉基米尔·普京要求不要发生这种情况，因为他试图在俄罗斯边境限制北约。

艾伯特说:“乌克兰已经加入了西方，加入了北约。”。“他们仍然有军事协议、条约、经济条约、商业条约或关系，尽管乌克兰与北约和美国之间没有北约条约。”

与俄罗斯接壤的北约成员国也表示担忧。乌克兰冲突对美国利益的潜在影响得到了考虑”有意义的美国外交关系委员会(Council on Foreign Relations)称，这场冲突“有可能导致美俄关系进一步恶化，如果俄罗斯扩大在乌克兰或北约国家的存在，冲突可能会进一步升级”。"

艾伯特说，随着俄罗斯试图“在大国游戏中重新确立自己的地位”，美国正在寻求维持欧洲的力量平衡，“保护乌克兰，使其成为抵御俄罗斯在欧洲入侵的缓冲区”，并指出乌克兰对俄罗斯、美国和北约具有“战略重要性”。

密歇根州立大学(Michigan State University)历史学副教授马修·波利(Matthew Pauly)是俄罗斯、乌克兰和东欧问题专家，他告诉美国广播公司新闻(ABC News)，北约“对美国的欧洲政策至关重要”，过去30多年来支持乌克兰“一直是美国对整个欧洲大陆安全政策的组成部分”。

“毫无疑问，最面向东方的北约成员国对俄罗斯在乌克兰的行动感到担忧是完全正确的，”保利说。“美国显然认为它有义务履行北约成员国的责任，守住北约东部战线。”

事实上，美国已经在俄罗斯入侵时出兵支持北约东翼。

“毫无疑问，美国将全力捍卫北约的每一寸土地，”拜登本周表示。"对一个北约国家的攻击就是对我们所有人的攻击。"

防止“世界大战”

美国已经派出了数千人增派部队尽管拜登已经明确表示，他不会派任何人去乌克兰打击俄罗斯，并强调了外交手段对实现降级的重要性。

在一个采访在本周早些时候与NBC新闻主播莱斯特·赫特的谈话中，拜登承认了进一步侵犯的风险。当被问及什么情况会促使他派兵援助乌克兰的美国人时，拜登说，“没有。当美国和俄罗斯开始互相射击时，那就是一场世界大战。”

“我们面对的是世界上最大的军队之一。这是一个非常不同的情况，事情可能会很快变得疯狂，”他说。

美国广播公司新闻部国家安全和国防分析师迈克尔·米克·帕特里克·马尔罗伊(Michael“Mick”Patrick mul Roy)本周在美国广播公司新闻直播(ABC News Live)上表示，冲突升级到乌克兰以外的风险“很高”。

“这应该是每个人都关心的问题，”他说。

维护民主和主权

保利说，美国参与这场危机的另一个重要方面是支持乌克兰作为一个民主国家。他说，自1991年乌克兰宣布独立以来，美国提供了“大量”外国援助，尤其是在20世纪90年代，以帮助乌克兰摆脱苏联时期，实现民主化并发展自由市场经济。

“乌克兰是一个民主国家，它是前苏联地区少数几个国家中唯一真正发挥作用的民主国家，”保利说。“尽管乌克兰的民主化道路颇具挑战性，但很难说这不是民主。”

“乌克兰的民主值得保护，”他继续说道。"民主是我们对抗战争的最佳保障，也是和平的最佳保证."

美国和西方盟友也表示支持乌克兰维护主权和领土完整，反对俄罗斯的侵略。

拜登说，美国一直在向乌克兰军方提供武器、训练和情报，以帮助其自卫。

“国家有权维护主权和领土完整，”奥巴马总统周二表示。"他们有自由设定自己的道路，选择与谁交往。"

在家的影响

入侵前线以外的确切影响仍不清楚。尽管拜登警告美国人民将会有“国内的后果”——最重要的是能源价格上涨因此。

“我不会假装这是没有痛苦的，”拜登周二表示。“这可能会对我们的能源价格产生影响，因此我们正在采取积极措施，以减轻我们自己的能源市场的压力，并抵消价格上涨的影响。”

GasBuddy的帕特里克德哈恩表示，在仅限于乌克兰东部的入侵中，油价可能会每桶上涨5美元或10美元。目前，每桶上涨1美元相当于全国平均油价每加仑上涨1.5美分。他说，如果美国及其盟友对俄罗斯实施严厉制裁，俄罗斯可能会通过限制石油出口进行报复，从而影响全球市场。

穆迪分析公司(Moody's Analytics)首席经济学家马克赞迪(Mark Zandi)表示，如果石油和天然气价格上涨导致美联储更加积极地收紧货币政策，这也可能会影响通胀。

网络战也仍然令人担忧。上个月，国土安全部警告美国对俄罗斯可能入侵的回应可能导致俄罗斯政府或其代理人对美国发动网络攻击。

随着更多的军事力量被部署来支持北约国家，这对美国军队也有影响。

艾伯特说:“我认为[美国人]应该注意这一点，因为这可能会极大地影响美国人员的战略部署。”。“如果没有其他事情，只是人们从他们现在的典型任务中转移到其他地方，更具战略地位，也许是为了抵御俄罗斯的入侵。”

Why Americans should care about the Ukraine-Russia conflict

After weeks of mounting tensions, United States officials have warned that a Russian attack on Ukraine could happen "any day now."

Russia has spent weeks building up military forces near eastern Ukraine, with more than 150,000 troops encircling Ukraine in Belarus and on the Russian side of the border, according to U.S. officials.

The Kremlin has denied warnings of an imminent invasion and claimed in recent days that it is withdrawing some troops, while U.S. and NATO officials have said -- and commercial satellite images have shown -- there have been no signs of de-escalation.

As global leaders continue to engage in diplomatic efforts to avoid war between Russia and Ukraine, a senior Department of State official told ABC News warned Thursday that this is "perhaps the most perilous moment for peace and security since the end of the Cold War."

As the conflict plays out on a global stage, Americans aresomewhat mixedon how the U.S. should respond. In anew poll from Quinnipiac University, 57% of Americans said the U.S. should not send troops into Ukraine if Russia invades, and 54% support Biden's decision to deploy troops to support NATO allies.

Earlier this week,President Joe Biden addressed the American publicand again made clear the U.S. will not send troops to support Ukraine. But he promised to defend "every inch" of NATO territory, already deploying several thousand more troops to Europe, and to support the Ukrainian people and their government with lethal defensive weapons, economic aid, and crippling U.S. and allied sanctions on Russia.

That high level of U.S. involvement is necessary, he said, because "this is about more than just Russia and Ukraine."

"It's about standing for what we believe in, for the future that we want for our world, for liberty, the right of countless countries to choose their own destiny. And the right of people to determine their own futures, or the principle that a country can't change its neighbor's borders by force," Biden said. "If we do not stand for freedom where it is at risk today, we'll surely pay a steeper price tomorrow."

NATO ties

To understand the United States' vested interest in the conflict, you'd have to go back to the Cold War, Craig Albert, an associate professor of political science and the director of Intelligence and Security Studies at Augusta University, told ABC News.

To counter Soviet aggression in Europe, the U.S. helped form the security alliance NATO, or the North Atlantic Treaty Organization, in 1949. In the years since, NATO has expanded several times, including adding three former Soviet republics.

Ukraine, a former Soviet republic that is bordered by Russia on the east, is not a NATO member, though in 2008 the alliance opened the door to membership. Russian President Vladimir Putin has demanded this not happen, as he seeks to limit NATO along Russia's border.

"Ukraine has attached itself to the West, to NATO," Albert said. "They still have military agreements, treaties, economic treaties, business treaties or relationships, even though there's no NATO treaty in place between Ukraine and NATO and the U.S."

The NATO members bordering Russia also present a concern. The potential impact of the Ukraine conflict on U.S. interests is considered "significant," by the Council on Foreign Relations, which said in part that the conflict "risks further deterioration of U.S.-Russia relations and greater escalation if Russia expands its presence in Ukraine or into NATO countries."

As Russia tries to "reassert itself into the great power game," the U.S. is seeking to maintain the balance of power in Europe and "protect Ukraine as a buffer against Russian-perceived aggression in Europe itself," Albert said, noting that Ukraine is "strategically important" for Russia, the U.S. and NATO.

NATO is "critical to U.S. policy in Europe," and supporting Ukraine for the past 30-plus years "has been integral to U.S. security policy for the European continent as a whole," Matthew Pauly, an associate professor of history at Michigan State University who is an expert on Russia, Ukraine and Eastern Europe, told ABC News.

"There's no doubt that the most eastern-facing NATO member states are quite rightly anxious about Russia's actions in Ukraine," Pauly said. "The United States obviously views it as its duty to oblige by the responsibilities of NATO membership to hold the line on the eastern front of NATO."

Indeed, the U.S. has already sent in troops amid the Russian aggression to support NATO's eastern flank.

"Make no mistake, the United States will defend every inch of NATO territory with the full force of American power," Biden said this week. "An attack against one NATO country is an attack against all of us."

Preventing 'world war'

The U.S. has sent thousands ofadditional troopsto Central and Eastern Europe in recent weeks, though Biden has made it clear he won't be sending any to Ukraine to fight Russia and has stressed the importance of diplomacy toward achieving de-escalation.

In aninterviewwith NBC News anchor Lester Holt earlier this week, Biden acknowledged the risk of further aggression. When asked what scenario could prompt him to send troops to aid Americans in Ukraine, Biden said, "There's not. That's a world war when Americans and Russia start shooting at one another."

"We're dealing with one of the largest armies in the world. It's a very different situation, and things could go crazy quickly," he said.

The risk of the conflict escalating beyond Ukraine is "high," Michael "Mick" Patrick Mulroy, ABC News national security and defense analyst, said on ABC News Live this week.

"It should be a concern to everybody," he said.

Preserving democracy and sovereignty

Another important dimension to U.S. involvement in the crisis has to do with its support of Ukraine as a democracy, Pauly said. Since 1991, when Ukraine declared its independence, the U.S. has offered "substantial" foreign aid, particularly in the 1990s, to help it emerge from the Soviet period, democratize and develop a free market economy, he said.

"Ukraine is a democracy, it's the only really functioning democracy of the few in the former Soviet space," Pauly said. "Although democratization has had sort of a challenging path in Ukraine, it's hard to argue that it is not a democracy."

"Democracy in Ukraine is worth protecting," he continued. "Democracy is our best guarantee against war and best assurance of peace."

The U.S., along with Western allies, has also voiced support for Ukraine maintaining its sovereignty and territorial integrity against Russian aggression.

Biden said the U.S. has been supplying Ukraine's military with arms, training and intelligence to help defend itself.

"Nations have a right to sovereignty and territorial integrity," the president said Tuesday. "They have the freedom to set their own course and choose with whom they will associate."

Impact at home

The exact impact of an invasion beyond the front lines remains unclear. Though Biden warned the American people that there would be "consequences at home" -- foremost anincrease in energy pricesas a result.

"I will not pretend this will be painless," Biden said Tuesday. "There could be impact on our energy prices, so we're taking active steps to alleviate the pressure on our own energy markets and offset rising prices."

In an incursion limited to eastern Ukraine, there could be a rise in the price of oil by $5 or $10 a barrel, according to Patrick De Haan of GasBuddy. Currently, a $1 per barrel rise equates to about a 1.5 cents per gallon rise in the national average price of gas. Should the U.S. and allies issue severe sanctions on Russia, it could retaliate by curbing oil exports, he said, impacting global markets.

If higher oil and gas prices cause the Federal Reserve to be more aggressive in its monetary tightening, that could also impact inflation, according to Mark Zandi, chief economist of Moody's Analytics.

Cyberwarfare also remains a concern. Last month, the Department of Homeland Securitywarnedthat the U.S. response to a possible Russian invasion could result in a cyberattack launched against the U.S. by the Russian government or its proxies.

There's also the impact on American troops, as more military forces are being deployed to support NATO countries.

"I think [Americans] should be paying attention to this because it could significantly affect strategic deployments of U.S. personnel," Albert said. "If nothing else, just people moving from where they are in their typical assignments right now, to move somewhere else, more strategically positioned against, perhaps, a Russian invasion."