What nation or empire lasted for the longest time?

Britsh Empire was the biggest the world has ever seen.

Longest i think goes to the Romans.

The Ancient Egyptian empire lasted the longest, but it was not the most powerful empire, nor the largest in size. It lasted for over 3000 years. There is some debate as to whether ancient Egypt could truly be said to be an empire as it did not expand in the sense that later empires did. This remains a matter of considerable debate.

Egyptians lasted longest

British were the biggest

Mongolian had the biggest mainland

The Roman Empire was most stable, first large-scale democracy and first republic. Best rags-to-riches story ever too.

China had the biggest population

The Athenian City-state invented democracy but was always tiny.

Sumerian City-states were the first civilization ever.