The passage of the 15th amendment in 1869 prompted the formation of two major suffrage organizations because

it granted formerly enslaved men the right to vote, while women were still denied this right.

Explanation:

The passage of the 15th Amendment in 1869 prompted the formation of the American Women Suffrage Association and the National Women Suffrage Association because women were left out of the amendment and did not have the right to vote. Later both would become the National American Women Suffrage Association.

The 15th amendment granted formerly enslaved people the right to vote, while women were still denied this right.