What prompted many southern yeomen and tenant farmers finally to support independence from britain in 1775?

The support was prompted when the Virginia royal governors promised to free any slaves who joined the loyalist

Explanation:

Until 1770s, the vast majority of Americans were not fighting for an 'Independent Country' and simply wanted more rights for local colonies.

However, gradually, as things became worse, more and more people found it better to fight for independence.

The Southern Yeoman and tenant farmers were mostly indifferent to the idea of Independence and did not mind being governed from London. In fact, the Yeoman were a celebrated military class which had roots in England and they felt a connection with the crown.

However, when the Royal Governors in Virginia actually proposed freeing slaves in support for Loyalist, it had a direct impact on the southern farming lifestyle, which was dominated by slave labor.

Both the Yeoman and the Tenant Farmers began to support and Independent United States.