What contributed the most to human migration more than ten thousand years ago?

sturdy boats were invented.
another ice age occurred.
a major volcano erupted in africa.
a severe drought occurred.

it may be touching on the issue of over sexualizing all women

a phrase from a poem by ralph waldo emerson about the battle of lexington and concord. emerson's words read, “here once the embattled farmers stood / and fired the shot heard round the world.”