The Mongols landed a settler/warrior pair on the tip of my island in 210 BC. This was unacceptable, so I declared war--and the archer I had on the scene died in the assault.

So, I paid the Ottomans and Byzantines to join in an alliance, and I sent some reinforcements to destroy the new Mongol town in 130 BC. Then I left the rest of the military action to my allies while I continued to settled my island. We signed a peace treat after the alliances expired, in 250 AD.
My contacts are completed with Japan in 50 AD and Sumeria in 100.
I had remained in Despotism, to get happiness from my garrisons, due to the lack of luxuries. I finally started the revolt in 150 AD and entered Republic in 270.
Was there a hidden restriction in this game set-up or did I find an unusual bug? Having researched Invention, I tried switching Zimbabwe's production to Leo's Workshop, but the game wouldn't let me do it! The icon was there, not grayed-out, but nothing would happen when I tried clicking it. Later, when the Sumerians and Japanese had already started it, it would let me switch, but I decided not to try racing them for it.
The Ottomans had left the marshes, directly across the strait from my island, unsettled. This proved to be a perfect spot for a bridgehead, so I sent workers to drain the marsh and settled a town there in 430. My naval actions would be limited to ferry duty across this strait, from this point on.
The Mongols demand Feudalism from me in 450 and declare war when I refuse, but we fight no battles before signing peace in 540. In 620, I decide to expand the bridgehead by declaring war on the Ottomans and this time I give the Mongol Monotheism to join in an alliance. In 720, the Byzantines ally, too. In 800, I trigger my GA with a victory with an Impi; these obsolete UU play no further role after this. The war proceeds, with one annoying revolt in Istanbul, until the Ottomans are destroyed in 1010.
Now my people have spices and incense and are ready for some peace. Researching ToG brings us into the Industrial Age in 1090.