Winston Duarte was the real mastermind with Marco being his tool, if you've read the books. The show hinted at it, but didn't cover the last 3 books. Duarte was

Winston Duarte was the real mastermind with Marco being his tool, if you've read the books. The show hinted at it, but didn't cover the last 3 books. Duarte was using Inaros to buy time to build up Laconia with alien weapons, while Earth/Mars dealt with the Free Navy and recovered from the attacks.