"6.15 If a major power has no corp within a minor country they have declared war on..."
Should read
6.15 If at the beginning of a diplomacy phase a major....
Or something similar, atm the manual basicly says that the war will lapse immidiatly and as its not allowed to declare war on any power that you have a corp in, a declaration of war against a minor would therefore lapse before you have the chance to move any troops.