It's April 19

Early on the morning of April 19, 1775, British troops marched out of Boston, Massachusetts (which they had occupied since 1768) with the aim of seizing "Military stores" laid up by Massachusetts militias  in Concord. They were met by those militias in various engagements at Lexington, Concord, Lincoln, Menotomy (now known as Arlington) and Cambridge. By the end of the day, those militias had lost 49 killed, 39 wounded, and five missing, while the British lost 73 killed, 174 wounded, and 53 missing. The American Revolution had begun.

On April 19, 1861, Union troops from Massachusetts, en route to Washington, DC on a mission not too terribly dissimilar to that of the British troops in 1775, came under fire from secessionist sympathizers while switching trains in Baltimore, Maryland. When the smoke cleared, four of the troops and 12 Baltimoreans lay dead.  Apart from one killed and one wounded in a cannon salute accident during the surrender of Fort Sumter a week before, it was the first effusion of blood in America's bloodiest war.

On April 19, 1943, resistance fighters in the Warsaw, Poland ghetto refused to surrender themselves and their fellow Jews to SS-Brigadefuhrer Jurgen Stroop's deportation/extermination force. It took nearly a month for the Nazis to overrun the ghetto (it had only taken them six weeks to conquer France!), murdering 13,000 and shipping more than 55,000 off to the death camps, with Nazi losses in the operation running somewhere between 100 and 300 killed and wounded depending on whose numbers you want to believe.

On April 19, 1993, the US Federal Bureau of Investigation used chemical and incendiary weapons, as well as gunfire, to murder 76 religious dissenters (about 25 of them children), outside of Waco, Texas.

On April 19, 1995, Timothy McVeigh used a truck bomb to murder 168 government workers, visitors, etc. (including 19 children at an on-site daycare center) at the Alfred P. Murrah Federal Building in Oklahoma City.

Remember.