The North Atlantic especially.
The whole Ming fleet story is absolutely fascinating. Points out perhaps better than anything else the differences between Chinese and European cultures, and why Western civ came to dominate the world.
Of course, we may be in the early stages of the process of surrendering everything we've built back to the barbarians.
This is another reason that I seriously doubt that the Chinese ventured to the Americas. Zheng He was Muslim, as were many of his men. They spread Islam everywhere they traded. There is no indication of Islam having been introduced (or even mentioned) anywhere in the Americas in pre-Columbian times.
Could you imagine if Islam had been incorporated into the Aztec or Mayan religions of the time? Shuuudddeeerrrr...