I understand that the Swedish were helping later because they were protestant, but why did the Spanish join to begin with? Also i wondered how the Spanish armies got to germany. They obviously must've travelled through France, how was this percieved by France?
They got there by way of " The Spanish Road" Spain/Hapsburgs held large amounts of territory in Italy, Netherlands and areas sprinkled through what's now Germany and France as well as the Hapsburg Austrians. Also at the time Spain had a gigantic navy for it's global empire. http://en.m.wikipedia.org/wiki/Spanish_Road . This shows you the actual route.
You may be interested in Geoffrey Parker's "The Army of Flanders and the Spanish Road, 1567-1659: The Logistics of Spanish Victory and Defeat in the Low Countries' Wars"