I have taken part in and run campaigns over many years. Some time ago, I came to the conclusion that you need to make a decision either to fight 'linked' battles or to run a multi-player campaign. In my experience things grind to a halt and fall apart where you try to do both, because you inevitably need to stop the campaign while battles are fought and "life intervenes".
I proposed a simplistic "campaign" mechanism in the third post of
this thread which basically allows people to use a very simplistic campaign-like mechanism to provide the backdrop for fighting battles. The principle being to allow people to make the strategic decisions that govern the size and nature of forces in any given sector so generating battles with uneven forces and slightly different objectives.