I'm not sure if Zulu is best for harder difficulties. On deity, your opponents start with some pretty strong defenders, and if you aren't careful you may end up spending a lot of turns waiting for the idea time to attack, while your opponent quickly builds more reinforcements.
Germany may be a better choice for the free +50% bonus to warriors, which if you are able to catch a few of their troops or barbarians off guard you can get blitz (multiple attacks per turn) or the +100% bonus to attacking cities and possibly even a general for an extra +50% (although the general takes more real time to move along with your group). Once you attack, you can expect your opponent to start building defenses as quickly as possible.
Also, make sure you don't go up against Greece.. they start with defenders that have a 3 defense.