Rivalry between the Liberal elite of León and the Conservative elite of Granada characterized the early years of independence and often degenerated into civil war, particularly during the 1840s and 1850s. Managua rose to undisputed preeminence as the nation's capital in 1852 to allay the rivalry between the two feuding cities. Following the start (1848) of the California Gold Rush, Nicaragua provided a route for travelers from the eastern United States to journey to California by sea, via the San Juan River and Lake Nicaragua. Invited by the Liberals in 1855 to join their struggle against the Conservatives, the United States adventurer and filibuster William Walker set himself up as President of Nicaragua after conducting a farcical election in 1856; his presidency lasted less than a year. Military forces from Costa Rica, Honduras, El Salvador, Guatemala, and Nicaragua itself united to drive Walker out of Nicaragua in 1857, after which a period of three decades of Conservative rule ensued.