What was the New Imperialism?

What was it? I think that the new empires were driven from a newer technological industrial engine, unlike the "old" imperialism which took had lesser tech like sailboats. The New imperialism had steamboats that could cut travel time in a sailboat. This means that the imperial powers can move quicker to mobilize troops and relay messages from home to colony. This quickness made colonizing and dominating faster. The old colonies in the Americas first struggled in the 1600s to fight back Amerindians and dominate the landscape because they had few numbers in the beginning and trips took months to cross the sea. In the new imperialism the imperialists can quickly go and send troops in regular weekly intervals instead of monthly intervals. That is why I think that the Americans won their independence by the fact that not enough British troops came to suppress rebellion at the same time. In India it was a the opposite. The Sepoy Rebellion shows that the British learned from there mistake in hate Unite States and quickly ended it. Am I emphasizing quickly enough? Alos another factor was better technology. The imperialists had repeating guns that could mow down old infantry charges. They didn't learn that it can be used against them and would be utilized when the big imperialist powers would fight in WWI.