So my sources come from a textbook, Civilization in the West: 7th Edition, by Mark Kishlansky.

The main factor for British Dominance was due to the Industrial Revolution. The people that the British conquered were very much weaker industrially, if they even were industrialized, which made wars with them very lopsided. The Idea of “New Imperialism” Sprang up in Europe because of this, because they could amass empires unprecedented in size extremely quickly, and have the communication and travel to maintain them. It was because of the Industrial Revolution that this could be done.

The UK was also so large because of India. The Dutch (which was the Netherlands) dominated trade in Asia, but through many mercantile wars between France and Britain they ceded India to the both of them, and during the Seven Years war in 1756 between France and Britain there was conflict in India which isn’t as well known, which resulted in the capturing of French ports in India. Because they had free reign in India it made them a lot of money, which allowed them to conquer the whole of it.

Lastly is the fact that the British had the Industrial Revolution First. They had an abundance of resources like coal and iron, which was an advantage over places like Germany as even though they had more of these resources it was divided by small fragmented powers as Germany wasn’t unified yet. I do not know how to exactly explain this, but they had a much freer economy. It allowed for the trading of ideas and the British were much more inventive because of it. Spain was very backwards in this as they actually required inventions to be approved by the state first. While the Early Industrial Revolution was not the sprawling urban areas and huge factories, the textile machines dominated the economy in America and the UK and grew them into the large powers during New Imperialism.

One thing that I do want to point out is that Britain wasn’t the only colonial Empire. Minus a couple of smaller colonial empires (I mean that they did not gain much land through colonialism, not that they were small) like Russia and Italy most powers took land that was vastly larger than their mainland country, and while I don’t know the exact sizes Algerian France was Nearly as large as Britain’s empire, and the Netherlands owned all of Indonesia, and they were able to do this because of how less developed many Asian and African nations were