In our Revolutionary War for freedom and independence from the tyrant King of England, our indispensable ally was the King of France.
In World War I, Woodrow Wilson said we were fighting to "make the world safe for democracy." Yet our foremost allies were five avaricious empires: the British, French, Italian, Japanese and Russian.
In World War II, the ally who did most of the fighting against Hitler was Josef Stalin.
Enough said. In America's wars, cold and hot, the enemy of our enemy has often been our ally, if not our friend.
And that is the question of the hour in the Middle East.
The region seems to be descending step by step into a war of all against all. And at its heart is the civil-sectarian war to overthrow the Syrian Alawite regime of Bashar Assad.
Now that war has spilled over into Lebanon and Iraq.
And in Syria and Iraq our principal enemies are the jihadists of the al-Nusra Front and ISIS, the Islamic State of Syria and the Levant.
Implacably anti-American, these Islamist fighters control enclaves in northern Syria and appear to have captured Fallujah and perhaps Ramadi, crucial cities of Iraq's Anbar province for which hundreds of Americans died.
And who are the foremost fighting foes of the Nusra Front and ISIS?
In Syria it is Bashar al Assad, whom Obama said two years ago must leave, and a Syrian army, which Obama was about to attack in August, until the American people rose up to tell him to stay out.
Who are Assad's allies against the al Nusra Front and ISIS?
Vladimir Putin's Russia, Iran, and Hezbollah whose forces helped turn the tide back last year against the rebels.
In Iraq and Syria, al-Qaida jihadists and Sunni terrorists, our enemies, are also the enemies of Iran, Hezbollah and Assad. Indeed, Iran has offered to join us in sending military assistance to Baghdad in its fight against the al-Qaida-backed rebellion in Anbar.
Yet, there are other vantage points from which this widening war is being seen, and one is Riyadh.
While Saudi Arabia has come to recognize the menace of ISIS and sent aid to rival rebel factions in Syria, the larger and longer-term threat Riyadh sees is Tehran. And understandably so.
Saudi Arabia is the Sunni and Arab power in the Persian Gulf. But Shia and Persian Iran is almost twice as populous and at the heart of a Shia Crescent of Iran, Iraq, Syria and Hezbollah.