The most likely reason for an increase in wars for independence later in the timeline is Europeans were not as willing to let these areas go easily.
As the 20th century progressed, many European powers were experiencing the aftermath of World War I and World War II, which led to a change in their attitudes towards colonial rule. Economic interests, strategic considerations, and a fear of losing global influence made many colonial powers more resistant to granting independence to their colonies. Additionally, the rise of nationalist movements and the spread of decolonization ideologies increased aspirations for self-determination among colonized peoples, resulting in more intense and organized struggles for independence.
While feelings of anger among Africans and advancements in weaponry did contribute to the dynamics of independence movements, the overarching resistance from European powers played a significant role in the escalation of conflicts during this timeframe.