1. Africa was very attractive to the European imperialists, and the reasons for that was that Africa was very rich in lot of natural resources, but most of the population was still living in a primitive manner and was not using them. Also, the Europeans saw that they will not have any big problem in conquering the African territories as they had superior military.
2. The United States, based on its strong economy, little by little was making a very large and strong army. It used the weakening of Spain, as well as Mexico's isolation, so it started to take over new territories and gradually becoming bigger and bigger.
3. Japan's imperialism lifted the economy, industrialization, and strengthened the military of Japan. The reason for such a development were the natural resources that it managed to gain from conquering new territories.
4. The officials of the Qing Dynasty in China were dealing with the foreign colonialism by corruption. They were taking money from colonial powers, giving them in return the Chinese ports for their own usage, thus maintaining peace, though the people were very displeased and frustrated with this kind of actions.