Hello there! Britain shifted from colonialism to imperialism because colonialism became too costly to maintain. The problems with colonialism included:
• Too costly/expensive. The damages of WWII (World War II) left Britain in massive debt, and many motives were present that influenced the rise of imperialism
• Giving up too much power. Britain, by participating in colonialism, was seizing their power simply because they and their rivals were in some sort of a competition for territory claims.
• Racial preferences. Britain transferred to colonialism due to what was called ‘Anglo-Saxon Superiority.’ This is exactly what it seems like; the early British highly favored racial superiority for Anglo-Saxons.
• Militia. The British military was thriving when switching to imperialism; a strong and powerful military was forming. With that came expense.
Britain shifted from colonialism to imperialism because colonialism became too costly to maintain. Hope this helps!