The most powerful was economic prosperity of European countries. They could exploit the land and the people of Africa and take their raw resources such as diamonds for example and take them to Europe. There they would be able to make goods with them and sell them to people for a lot of money and this meant that they would grow vastly richer than they were before.
Watt attempted to commercialise his invention, but experienced great financial difficulties until he entered a partnership with Matthew Boulton in 1775. The new firm of Boulton and Watt was eventually highly successful and Watt became a wealthy man. In his retirement, Watt continued to develop new inventions though none was as significant as his steam engine work.