Why were tropical rainforest societies less able to resist colonial invasion than centralized savanna kingdoms?

In the region now known as the Democratic Republic of the Congo, the ability to resist colonial invasion was significantly influenced by precolonial social and political structures.

In the tropical rainforest, ecological conditions presented formidable obstacles to the formation of large, centralized states. Consequently, these areas were dominated by small-scale, segmented societies organized into village communities and corporate groups. This decentralized structure meant that these communities lacked the unified political and military apparatus necessary to coordinate a large-scale defense, which hindered their ability to resist colonial forces.12

In contrast, the southern savanna region developed centralized state systems, such as the Kongo kingdom and the Luba-Lunda states. These kingdoms possessed elaborate political institutions and were more adept at acting in a concerted manner. However, their resistance to colonial encroachment was ultimately undermined by internal fragmentation, the destabilizing effects of the slave trade, and the introduction of sophisticated firearms by outsiders.12