The Napoleonic Wars changed Spanish military history dramatically; the Peninsular War saw the development of guerrilla warfare against the occupying French forces. The collapse of central Spanish authority resulted in successful wars of independence amongst Spain's American colonies, drastically reducing the size of her empire, and in turn led to a sequence of civil wars in Spain itself, many fought by frustrated veterans of the French and colonial campaigns. Attempts to reassert imperial power during the mid-19th century, enabled by the development of the steam frigate ultimately failed, leading to the collapse of the remnants of Spain's empire in the Americas and Asia in 1898 at the hands of a rising power, the United States of America. The political tensions that had driven the Carlist Wars remained unchecked, spilling over once again in the Spanish Civil War of 1936–9. Bringing a foretaste of the tactics of the Second World War, several nations used the conflict as a testing ground for new aerial and armoured warfare tactics. In the post-war period, Spain has increasingly turned away from the last remaining colonial conflicts in Africa, and played a growing modern military role within the context of the NATO alliance.