Verified Answer :

To recruit more troops, conscription was adopted to fill the
ranks, new weapons were developed.
During the course of the war, the Union also offered incentives to
encourage more recruits.  New
technologies were introduced and Northern industry was booming. The South still
relied mostly on agriculture and though recruitment was high initially, it
later decreased as the war dragged on.

Answer:Fort Sumter - it was the start of open combat between North and South

Battle of Antietam - 26,000 people die - bloodiest day in US history

Explanation: Hope this helps :)