Huh?
By "political system" I would hope you werent referring to democracy. Its much older than the US. But I'll assume you knew that.
What I think youre saying is, America's political landscape was shaped entirely different from Europe over the past century or so because we have never fought a war on our soil.
And while I have never looked at it that way, I am inclined to agree. Losing 20% (another 20% wounded or so) of your male population in less than 10 years has a way of changing the very iden y of your nation/continent.
As it were, I am not swayed one way or the other on which system is better. What I do know is the combined European Union is kicking the USA's ass economically. It finally took over as the largest GDP in the world (at least, I just noticed anyway).
What I do know is that I love my country, but hate my government. I dont care if theyre Republican (conservative) or Democrat (liberal). I hate politicians, I hate bureaucracies, I hate secrecy, I hate class warfare, I hate greed, I hate everything every government stands for the world over.
They are nothing more than a necessary evil, because humans in general are the most notoriously inhumane animal the world has ever seen. Left to our own devices with no authority, we'd all be enslaved to someone who won more than we did eventually.
War shapes everything in history, no different then to now. But there hasnt been a single, unified power in the history of man as militarily powerful as the United States. Rome at its height is of no comparison, militarily speaking (maybe even culturally).
As it were, I agree with your point that our political landscape was shaped in a vacuum in comparison to Europe's. But then again, we didnt have the constant neighbor-aggression Europe lives/lived with and glaring cultural/language differences only a few hundred/thousand miles away from one another.
I personally feel America has nothing in common with Europe beyond NATO. Europe's problems should be just that....Europe's problems. Because outside a military agreement, the EU is as large a compe or to the US as China (economically speaking). So IMO, our relationship with Europe is nothing more than "the enemy of my enemy is my friend".