The primary motivation for many African Americans, both enslaved and free, to fight in the Revolutionary War was the hope that their participation would lead to the end of slavery. Many believed that by fighting for freedom and helping to achieve independence, they could also work towards their own liberation and that of their fellow enslaved people. Additionally, some also sought military rank and opportunities within the military, while others may have feared punishment if they did not fight. However, the desire for freedom and the hope for a better future were significant motivating factors for many.
Thus, the best response from your options is:
they hoped the war would end slavery.