Robert Silverberg 
Gate of Worlds 

From Turkish dominated Europe, across the high seas to the land of opportunity – the Aztec Empire. Dan Beauchamp is a young Englishman whose heart longs for fortune and adventure. But industrial Mexico is a long way from primitive Britain, and Dan has a lot to learn. From the city of London – better known as New Istanbul – to the untamed wilderness of North America here is a high adventure not to be missed.