An Armed Civilian population in America protects the whole Free World's very existence

Why?

Because governments and militaries become corrupted over time. Unfortunately, the most likely militaries to be corrupted are voluntary militaries where there is no draft. Strangely enough, having a draft tends to make a military more honest (at least in democratic nations) for a variety of reasons.

Look right now at how incredibly corrupt the Executive Branch under TRump is. I think there is over 7 to 20 billion dollars in wealth just tied up in the executive branch not including whatever Trump is worth for the most wealthy Executive branch in U.S. History. And this will tend to corrupt the executive branch more and more (at least during Trump's Stay in office).

Why?

Because money is power or more precisely "Money Buys Power" of all kinds both good and bad.

So, because of the force of all this money it corrupts people all over the world through the executive branch of the U.S.

But, wasn't this always true?

Yes.

But, this is to the most extreme level of corruption we have ever seen in regard to the White House and the executive branch of Government to the point where we understand that Trump doesn't care about the rule of law or equality at all. He only cares about how much money he and his family and friends can make while he is president and after. That's ALL Trump really cares about here on earth.

So, what protects the Free World and all it's democracies from military takeover and complete collapse?

A fully armed and educated American Populace is the ONLY thing that really protects democracies around the world at all (from a worldwide perspective).

Because anyone attacking the U.S. would be out of their minds to attack the U.S. with any army because American citizens would just become snipers and pick them all off from a distance one by one.

I suppose you could nuke the U.S. out of existence completely (the lower 48) but you would still have Americans in Alaska and Hawaii and any other U.S. places picking foreign army members off for years after that too.

So, an armed civilian populace in the U.S. in the end is the ONLY reason the Free World Continues to be free!