Overall, European imperialism weakened after World War I. The war led to the end of several empires and left the others in debt. More colonial populations used the war's end as an opportunity to advocate for self-rule.
Despite this, there were many European imperialists who continued to promote imperial agendas. The imperialist nations used a number of rationalizations. Some even pointed to WWI itself as justification. They argued that European imperialists needed to protect their colonies from exploitation by other imperialistic nations. WWI, they said, proved the lengths that other nations would go to exploit overseas colonies and take over others. Ironically, colonizing nations saw themselves as protectors of their colonies from other imperialists.
This period of imperialism was also marked by notions of racial superiority. Social Darwinism was an oft-promoted concept. Many imperialists continued to argue that "might makes right." Their power and ability to take control of these colonies and subjugate other races was a sign that they were entitled to do so. This concept existed before WWI, but it gained more traction after the war.
However, as stated above, imperialism overall greatly weakened after the war. Many Europeans began to realize that the age of great empires was coming to an end. While most still believed that they should continue to keep their colonies, they felt that their role as imperialists should change. British policymakers, in particular, began advocating for greater political and administrative involvement by their colonial subjects. In Africa and India local populations were granted a more active role in their governance. Many British imperialists thought that they were being benevolent protectors by extending limited amounts of self-rule. They saw it as a way to share "civilization" with their colonial subjects. They even thought it would appease independence-minded colonial subjects.
However, this backfired in many ways. In a number of places, particularly in India, once locals began administering their own affairs, aspirations towards self-rule and independence increased. Most colonies did not become independent for another generation. Still, the move towards local empowerment helped to hasten the end of imperialism.