Final answer:
The death of Major-General Robert Ross was critical because it halted the British momentum at Baltimore, led to a failed assault, and demoralized his troops, contributing to the British decision to retreat and the subsequent defeat at the Battle of New Orleans.
Step-by-step explanation:
The death of Major-General Robert Ross was a critical loss for the British during their campaign in the War of 1812, particularly during their advance on Baltimore. When Ross was killed by American snipers, the momentum of the British offensive was significantly hindered. Ross was leading 5,000 troops in an attempt to secure Baltimore, a strategic target, but after his death, the troops faced stiff resistance and the British were ultimately forced to retreat without achieving their objectives. This incident weakened British resolve and highlighted the impact of losing a key leader during a military campaign.
The death of Ross also had an effect on the British psyche. Following his loss, the British troops were less effective, leading to a failed attack in Baltimore. The subsequent retreat signaled a broader loss for the British efforts in the war, as they also faced defeat at the Battle of New Orleans. This was despite the Treaty of Ghent — which effectively ended the war — already having been signed, although it had not yet been ratified by the American Government.