Vox reader Jo Ní Coinnigh asks: Why do American politics (especially the presidential election) affect not just the US, but the entire world?

On one level, the answer to this question is very simple: The United States is the most powerful country in the world. So what happens in Washington matters to the world in the same way that decisions in Rome during the height of its imperial era mattered to everyone who lived near its borders.

But I worry the comparison to Rome actually undersells the importance of America to the world. Because while the ancient world was more interconnected than most appreciate, it was nothing compared to the world we live in today.

Partly, of course, this is a matter of technology — starting with the most dangerous weapons ever made by humanity.

Post-World War II politics have been largely defined by the specter of nuclear war, a conflict so devastating that it cannot conceivably be won. Were the United States go to war with Russia or China — or even North Korea — any use of nuclear weapons would have consequences going well beyond the targets. A full-on nuclear exchange between large nuclear powers could even undermine the foundations of life on earth itself.

But even if we aren’t talking about the worst case — and, frankly, improbable — scenarios, the United States is still a global hegemon, setting the terms of political engagement for nearly everyone on the planet.

It is the most powerful country in the NATO alliance, which is the largest alliance system in global history. The US........

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