Why did Henry V besiege Harfleur?

Henry V besieged Harfleur in August 1415 as part of his campaign to reassert English claims to the French throne and territories. Following the rejection of his substantial territorial demands by the French, Henry arrived in Normandy with approximately 12,000 men to press his claims.1

The siege was a strategic component of his broader effort to renew the Hundred Years’ War, a conflict driven by disputes over the legitimate succession to the French crown and the ownership of various French lands. While the city capitulated within six weeks, the siege proved costly, significantly diminishing Henry's forces due to casualties, desertions, and disease before he continued his march toward Calais.1