How did early humans migrate into North America? They fled wars in South America by escaping into North America.
They sailed from Europe to North America.
They crossed a land bridge that connected Asia and North America.
They traveled in small boats from Africa to North America.

The last one

Explanation:The Americas were the last (well, second-to-last if you count Antarctica) continents to be inhabited by early humans. Archaeologists estimate that people entered North America by crossing over the Bering Strait, which back then was a wide swath of land, about 15,000 years ago. In other words, people got here by walking a very long distance.

Ancient Greece, which comprised numerous city-states, had implemented direct democracy as a system of governance. The Greek civilization was a first ever ancient civilization to have introduced democracy; the system that was unparalleled during that time.