If US seeks to absorb a neighboring country by force, do you think any country can stop it? US will absorb a neighboring country in a few months at most.
The short answer is, if we invade any of our neighbor, like Russia did, there are no way anyone can stop us. People keep saying "What could US do when they can't even get rid of Taliban" First of all, US uses probably less than 1/10 of its military might in Afghanistan, the peak troop level in Afghanistan is 120,000 troop, that's less than 1/10 of the 1,280,000 strong US Army, and then I did not even factor all other branch into this equation. Not to mention, Afghanistan is 13,000 mile from US Mainland, and at least 4000 miles from the closest US military base, so that war is not even a conventional war, it's an expedition.
So it is extremely naive to think Afghanistan can be anything of a reflecting point of the true combat power to the United States Military, however, that said, there is one major factor that stop us from using all our might in battle, and that factor is not Russia, nor Chinese nor any military in the world, but the United States Congress.
There are only ever 1 time when US put all its military might in any war (Not counting War of Independence and Civil War), and that's World War 2. This is when the US went in 100%, the problem is not that we devoted every division, every fleet, and every squadron of fighter, bomber etcl, but the US went in and shred EVERYONE off their constitutional right, the media blackout, the interning of Japanese and Germany citizens or even American Citizens of Japanese and German heritage, the violation of due process clause, the violation of 1st Amendment right, the violation of 5th and 6 amendment right, all these happened during WW2. And that thus give the US Government the ultimate power to utilise the entire military might in a war over any civilian opposition, that was not heard of before and after.
In today term, I don't think US would ever again going to war like Ukraine does now, not until someone else decided to fancy a go at the US and attack US territories in country or overseas. But still, even at 1/10 or 1/5 (probably the ceiling amount we can do in any war now) would still a force to be reckon with.
And we have such a liberal congress and president most likely because US is the sole Superpower at this point, and there are no need for a hawkish stance, but it would be another story, if this US led International Order is being altered. You can bet we will look less toward civil liberty and more hawkish if that is the case here.
