Over the past few years, Britain and the American colonies didn't have any sort of positive relationship. Taxes were placed, and the colonies were forced to pay without any word of their own.
April 18th, 1775, the king sent British troops to seize a stash of weapons in Concord. He had another mission for them as well, to go to Lexington and arrest the leaders of the Sons of Liberty.
Spies were able to send the information to the colonies about the arrest of the two rebels. Three people were sent to deliver the message to them at Concord, though only one of them made it all the way to Concord.
After the leaders of the Sons of Liberty escaped, the next day a whole swarm of British soldiers met with a handful of minute men. No one knows who shot first, but the battle ended with eight fewer minute men.
After they won the battle, the British continued to Concord to destroy any weapons. There was no big issue and they destroyed the weapons they found. Little did they know that there was plenty hidden.
The British were also unaware of the fact that hundreds of colonists were waiting on the other side of the North Bridge. The British fired first but retreated after the militiamen fired back.