In the wars she has fought, America has often allied with regimes that represented the antithesis of the cause for which we were fighting.
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.
Moreover, Riyadh in 2013 saw her superpower patron, America, back away from an attack on Syria, negotiate in secret with Iran, and begin talks with the Ayatollah's regime on limitations to its nuclear program — in return for a lifting of U.S. sanctions.
To the Saudis, what appears to be an emerging detente between Tehran and Washington looms as a strategic disaster.
From Israel's vantage point, the overthrow of Assad would mean the isolation of Hezbollah, which would no longer receive weapons from a Syrian regime that Hezbollah had fought to keep out of power.
But what about America's point of view?
"Sooner or later," The Washington Post writes, "the United States will have to face the threat to its vital interests emerging across the Levant."
But, with due respect, there are no U.S. "vital interests" in the Levant.
For the first 150 years of our existence as a nation, the Levant was ruled by Ottoman Turks, and then by the British and the French under the Sykes-Picot Agreement of 1916.
What difference did it make to us who ruled Damascus or Beirut?
The vital interest America has in that region is to keep the oil flowing out of the Gulf, upon which the global economy depends.
While a victory for the rebels might fit well with the agendas of Riyadh and Tel Aviv, it might also mean a massacre of Alawites and a mass exodus of Christians. At best, it would bring about a regime along the lines of the Muslim Brotherhood government that lately ruled in Cairo. At worst, it could bring to power a regime dominated by Sunni jihadists.
The greatest threat to U.S. interests there is not autocrats, Sunni or Shia, interested in getting rich, but radicals with the mindset of suicide bombers taking over a state and spreading revolution down the Gulf.
War is the clear and present danger, and peace the necessary condition of securing those interests.
The defeat of ISIS in Anbar and Syria and peace in the region should be our primary goal. And if Iran is willing to assist Damascus and Baghdad in defeating al-Qaida, Iran should be treated as a temporary ally in a common cause.
After all, FDR and Truman got on famously with "good old Joe" Stalin.