Why does China is persistent on grabbing lands in neighboring countries?

First, it is presumptuous to claim that a country is “persistent on grabbing lands in neighboring countries” just because there is a land dispute. Perhaps China is correct and it is the other countries that are attempting to grab land from it. Second, the disputes rest on China’s historical claims to the regions in question. China claims all of the lands that have ever been part of China to still be under its control, in part because it has never been party to any agreement severing any of the disputed lands from its territory.

Take, for instance, the dispute over Arunachal Pradesh. This is a region that was traditionally claimed by China and ceded to India by Tibet, but China claims that Tibet had no right to cede the territory in the first place (because Tibet is itself claimed by China, and the Lhasa government is not considered fully legitimate by the Chinese government even if they cannot always keep the Tibetans under control). In China’s view, Tibet had as much authority to transfer Arunachal Pradesh as I have to sell the White House to France.