Final answer:
The major event in Europe during the summer of 1789 was the French Revolution, which inspired the Haitian Revolution that led to Haiti's independence in 1804.
Step-by-step explanation:
In the summer of 1789, while Haiti was still the French colony of Saint-Domingue, the major event happening in Europe was the French Revolution. This monumental event provided the intellectual foundation and inspiration for the Haitian Revolution that commenced in 1791. While the American Revolution had solidified slavery and empowered American slaveholders, the French Revolution's ideals of liberty, equality, and fraternity sparked slave rebellions in the Caribbean, leading to a series of historical events which would eventually culminate in Haiti becoming a free republic in 1804 after a successful slave uprising led by figures such as Toussaint Louverture and Jean-Jacques Dessalines.