Istanbul is a beautiful city sitting astride the Bosphorus. A sophisticated, tolerant city, it seamlessly mixes Occident and Orient. But now it has been stricken by the new cancer of our age: terrorism.

The attack on two Turkish synagogues is not just an instance of terrorism. It is the deliberate targeting of civilians nowhere near a war zone. And it reflects the virulent anti-Semitism that has despoiled our world for centuries.

It is hard for most people steeped in the humane, liberal values of Western Civilization to understand the massacre of innocents. To slaughter to make a political point. But terrorism is not likely to disappear.

Indeed, it is a surprisingly common practice. Although Americans were taken unaware on September 11, many other peoples have long suffered from the murderous attention of domestic and foreign terrorists.

The attacks on Israelis have been frequent, in Israel and around the world. And killings continue, deterred neither by war measures nor peace processes.

Kurdish rebels used terrorism against the Turkish government. Urban leftist terrorists once bedeviled Germany and Italy. Ethnic and religious separatists have killed in Northern Ireland and Spain.

Terrorism was a tool of leftists fighting military regimes in South America. Communist guerrillas routinely bomb urban targets, such as bars and nightclubs, in Colombia.

Chechens kill in Moscow. In Algeria, terrorism was used against the French colonial overlords and continues today against the military-backed regime.

Tamils and Sikhs kill in India. Tamils also have routinely deployed terror against the majority Sinhalese in Sri Lanka, making the former the most prolific suicide bombers on earth.

Russian revolutionaries once killed czars and czarist officials. A Serbian terrorist shot down the Austro-Hungarian royal heir and his wife, triggering World War I. No other murder in human history — except perhaps that of Julius Caesar — had such profound consequences.

Terrorism is common, and will persist, because it is a tool of the weak versus the strong, a cheap military weapon to achieve expensive political goals. As long as there are people willing to kill to advance their ends, there will be terrorists.

Awful but unsurprising are attacks on military targets, such as the Marine Corps barracks in Lebanon, the USS Cole on its visit to Yemen, and the Italian military-police headquarters in Iraq. Lacking the conventional weapons of war necessary to resist, opponents turn to the truck bomb. Horrific, careless of noncombatants, and brutally effective.

The Istanbul strikes — like those in Riyadh, Jakarta, Bali, and on the World Trade Center — take terrorism a step further. They are intended to kill noncombatants. The goal is not to resist foreign military power per se, but to murder and terrorize civilians. The willingness to kill, and kill indiscriminately, is expected to cow peoples and governments.

Yet the bombings of the two Turkish synagogues cap the murder of innocents with that age-old disease, anti-Semitism. It’s been around for centuries, mixing discrimination with persecution.

The early variants were practiced in the name of Christianity, a bizarre justification of what was in fact a murderous assault on the roots of Christianity itself. Without the Jew Jesus, there is no Christianity. There is certainly nothing in his message to justify the Spanish Inquisition, Russian pogroms, or the polite social ostracism often practiced in Western Christian societies.

Today, Christians, especially American evangelicals, have become among the strongest defenders of Judaism, even occasionally confusing support for Israelis against Palestinians with support for Jews against persecutors. Nevertheless, a Christian commitment to the life and dignity of all those created in God’s image is the strongest barrier possible to anti-Semitism: The most monstrous anti-Jewish attack ever, the Nazi Holocaust, grew out of a movement that assaulted authentic Christianity with the same fervor that it destroyed tolerant humanism.

That terrorists claim to kill people in the name of God may be the greatest sacrilege. The Abu-Hafs al-Masri Brigades, a group linked to al Qaeda, took credit for the Istanbul attacks: “The remaining operations are coming, God willing, and by God, Jews around the world will regret that their ancestors even thought about occupying the land of Muslims.”

What kind of God urges his people to kill other people gathered to worship him? What kind of God urges people to kill other people today because of what their ancestors did years, decades, and centuries before? What kind of God urges people to kill other people, made in his image and of transcendent worth, to advance ephemeral political ends?

What kind of God is this?

If this is not the God of Islam, Muslims must speak out. Not just Islamic politicians themselves under attack — in Indonesia, Saudi Arabia, and Turkey, for instance. But clerics, imams, teachers, and ayatollahs. And common celebrants, those who regularly fill mosques for worship and daily drop to their prayer rugs.

Moreover, it is not enough to denounce attacks on Americans or Australians or Indonesians. It is necessary to denounce attacks on Jews. To say clearly that the God of Islam does not urge the children of Ishmael to murder the children of Isaac.

No one but the enemy gains from turning the war on terrorism into a war between civilizations. But it certainly is a war between the civilized and uncivilized. And after atrocities like that in Istanbul, it is essential that Muslims as well as Christians declare against anti-Semitism, the blasphemy that refuses to die.