Conversation so far:
What did Zheng He do in China
Zheng He was a Chinese mariner, explorer, diplomat, fleet admiral, and court eunuch.
why did Imperial officials say Zheng He was not important
It is likely that the expeditions – unauthorized by (and in fact, counter to) the injunctions of the dynastic founder – presented a kind of embarrassment to the dynasty.
why did Ming naval efforts decline after Zheng He's voyages
The expenditures necessary for land campaigns directly competed with the funds necessary to continue naval expeditions.
what land campaigns were there in China after Zheng He's voyages
China launched annual military expeditions from Beijing to weaken the Mongolians.

Question: why were they fighting the mongolians
Self-contained rewrite: why were the Ming Chinese fighting the mongolians