Considering all the time between Melkors capture and release, Sauron had time to build the most largest army to ever walk arda.
Considering over 3,000 years passed, i find it probable that once Morgoth returned, he had a entirely built up army of 8-10 million orcs ready for war, a fully repaired Angband, he was ready for war.
So essentially, Morgoth really owes it to Sauron.