What events led up to D-day

Why was it difficult fpr unions to succeed in the 1800s

Ineed asap! ! what is the name of the system in which each branch of the u.s government can limit the actions of the other branches? a. perpetual union b. division of powers c. cooperative federalism d. checks and balances

Which describes a contribution from classical rome to modern western civilization? a. international gathering to celebrate sporting achievement b. written constitution based on natural rights c. large infrastructure projects to benefit the public d. direct election of the ruler by all residents of the empire