European rivalries appeared most often as commercial competition, and in 19th century Africa, that included the right to move goods by steamboat along rivers. The British had a head start thanks to their early adoption of steam technology and their supremacy on the high seas. They became the strongest proponents of the principle of "free trade" which prohibited countries from creating legal barriers to another country's merchants. Occasionally, Portuguese leaders resisted, but the British alliance provided sufficient benefits to convince various administrations to go along (although they faced revolts at home and in their colonies).