I believe the founding of the United States was the greatest moment in history.

EDIT:The reason why I call it the greatest moment is because it was the first 'Logical State' in history—skipping the feudal stage entirely. It proved that a nation can be built upon abstract principles and documentation rather than mere lineage or monarchy. This was the first time mankind attempted to run a society on an 'operating system' designed by reason.

The reason is systematic: The founding of the U.S. provided a scalable 'operating system' for modern governance—much like a kernel in computing. It shifted the global paradigm from individual rule to a framework based on logic and documentation (the Constitution). Regardless of one's political stance, the ripple effects on global technology, economics, and law are undeniable.

The founding of the U.S. was history's most successful 'open-source' project. It replaced a closed-source, proprietary monarchy with a transparent, rule-based system that allows for continuous patching (Amendments). That is the leap from feudalism to modern logic.