Conversation so far:
What did Zheng do in China?
Imperial officials minimized the importance of Zheng He and his expeditions throughout the many regnal and dynastic histories they compiled.
why did they say he was not important?
State-sponsored Ming naval efforts declined dramatically after Zheng's voyages.
why did it decline?
The expenditures necessary for these land campaigns directly competed with the funds necessary to continue naval expeditions.
what land campaigns were there?
At considerable expense, China launched annual military expeditions from Beijing to weaken the Mongolians.

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