The reason Sauron wanted to conquer Middle Earth... my theory...

[Eönwë]

Originally Posted by Morthoron

What the question would be is which way the Orcs might go (and argument could be made for either Sauron or Morgoth).

Probably Morgoth. He made them after all. Sauron is just "borrowing" them, or "keeping them safe". They're not actually his to command, if Morgoth was the other option.