Which factor played the greatest role in making world war l one of the deadliest conflicts in human history?

I would say the invention of new technology such as the tank, machine guns, and other weapons made every attempt to gain yardage in trench warfare very bloody costing hundreds of lives for every yard gained or lost.

why was the national assembly formed by the third estate?

the estates-general had not been assembled since 1614, and its deputies drew up long lists of grievances and called for sweeping political and social reforms. the third estate, which had the most representatives, declared itself the national assembly and took an oath to force a new constitution on the king.

c. the king has significantly abused the colonists' rights many times over a long period of time.