What's really changed since then is that government has grown unimaginably larger than the forefathers ever imagined possible, let alone intended. And we've also massively increased the power of various branches. For instance, that the president alone can now unilaterally deploy our military throughout the world is just insane and arguably completely unconstitutional. In any case it completely destroys the entire system of checks and balances that our system, and country, was built and prospered upon.
I'm not entirely sure what you mean by system such as ours failing, nor that our system was kept afloat by tradition. We started a revolution against a heavily centralized mercantalistic monarchical empire to create a decentralized capitalistic democratic republic.
I'm not saying it's temperance that keeps the US together (except for the first 8 years) but rather tradition. Long standing institutions tend to amass legitimacy over time.
It's not so much that we have a larger country these days as that we have ideologically distinct parties. We had real ideological distinctions between the Democractic Republicans and the Federalists in the old days and in addition to what you mention there were people considering a military coup if the election of 1800 went the wrong way. Thankfully the Federalists imploded and for a long time parties were mostly patronage machines, though you did have the pro-science, pro-religion, pro-treating other races with respect party versus the pro-freedom, pro-small government, pro-treating other religions with respect party as sort of vague ideologies. Except for the bit where they polarized over slavery and we immediately had a civil war. After progressive reforms made patronage less of an issue the two parties were both still ideologically mixed until the South defected to the Republicans and things have been polarizing ever since.
Right now we're in a situation where the most conservative Democrat in Congress is more liberal than the most liberal Republican, a situation that is basically unprecedented. I don't expect the current system to break soon, hundreds of years of tradition is pretty resilient, but if the current level of partisan divide and constitutional hardball continues it will break down eventually.