This map had 8 civs, including me, Roosevelt (Friendly), Gandhi (Roosevelt's vassal)(Firendly), Suryavarman (my vassal), Justinian (my vassal), Saladin (my vassal), Joao II (my vassal) and Zara Yaqoob, the wonder hog. Now, I and my vassals controlled much more than half of the map and still had NO Aluminium. Also, oil was very scarce. So, I had to go for the civs who had oil first - Saladin and Joao II. They were also much weaker than Zara. Also Roosevelt and Gandhi had been very friendly towards me and combined, they had quite a lot of units. Attacking Zara was the easier route IMO.