Was England justified in going to war with the American colonies?

The American colonies rebelled against their lawful government, so the British did not regard themselves as being 'at war'. They were quelling a rebellion and fighting terrorism. They knew didn't have the resources to stop American secession in the long term, especially as the Dutch and French took the opportunity to wage war in Europe, so the fight was somewhat half-hearted on the British side. Many, if not most, 'Americans' were British emigrants, after all.