The War of 1812 was inspired by a couple of events. The impressment upon people found on American ships was a contribution, as well as the Embargo Act and Non-Intercourse Act, and struggle over land. These three events caused fighting between Britain and the United States.
The British passed a series of laws which allowed them to seize ships. While seizing American ships they found British Navy men who had left and gone to America. The British impressed these "deserters" to serve on British war ships. This outraged the Americans because they felt that this violated the United States' Neutrality Proclamation.
The Embargo Act against Britain banned trade with all foreign nations. This was made to affect Britain and France yet it hurt the American merchants. The Non-Intercourse Act was then put into effect. This banned trade with only Britain and France and would restore trade with whatever side obeyed the U.S.
neutrality, first. This did not make Britain and France as hurt as it was meant to. This whole ordeal of no trade then some trade mad the merchants mad.
The struggle over land in the Northwest Territory was caused by Britain. The Indians were rebelling against the United States' growth in ownership of land. The British knew this and found that it was easy to help the Indians by giving them supplies and soldiers to fight the U.S. This made the Americans even more outraged.
These three reasons outraged both the United States and Britain. This gave enough reason to both to start a war. United States Congress declared war to rid themselves of British insult.