R.U.S.E.

After finishing the story, you should have anywhere from 2000-4000 enemy unit kills (I had 3895) which doesn't leave you with that great of an amount to gain.

The easiest way I found to do this, was to do it whilst using the Triangular Diplomacy method for grinding 'War God' as all the supply caravans count as a kill, and you kill quite a few each map. This method is simple, set your nation as the UK and the Map Triangular diplomacy (3 player). Select two AI's both at medium and set them as Prototype so they try to build the most expensive structures first.

As soon as the match starts, build an airport and then send 4 paratroopers to each of the enemies bases but do not capture their main base. These paras should stop all the supply caravans that pass them trying to get to the enemy headquarters, and just leave them for about 15 minutes until all the enemies supply bases have dried out. Then simply capture all the enemies buildings and you will get a victory, as you win more, the bonus streak will also increase the exp you receive.

Rinse and repeat and you should get this and be on your way towards 'War God' in no time.