CARACAS, Venezuela — As the price of oil roared to ever higher levels in recent years, the leaders of Venezuela, Iran and Russia muscled their way onto the world stage, using checkbook diplomacy and, on occasion, intimidation.

Now, plummeting oil prices are raising questions about whether the countries can sustain their spending — and their bids to challenge United States hegemony.

For all three nations, oil money was a means to an ideological end.

President Hugo Chávez of Venezuela used it to jump-start a socialist-inspired revolution in his country and to back a cadre of like-minded leaders in Latin America who were intent on eroding once-dominant American influence.

Iran extended its influence across the Middle East, promoted itself as the leader of the Islamic world and used its petrodollars to help defy the West’s efforts to block its nuclear program.