Most modern believers see the success and spread of their religion as the result of spiritual activities such as preaching and conversion. And this is certainly true. But it is equally true that victory in battle has often had a decisive impact in the success or failure of religions.
Throughout ancient and medieval history, most believers maintained that God — or the gods — would grant victory in battle to the faithful. Indeed, it was generally assumed that no one would want to worship a God who could not protect his people. Defeat in battle was viewed either as a failure of a god in the face of more powerful deities or as evidence of the believers' inadequate obedience and devotion to their god.
The rise and fall of ancient religions was often intimately linked to the military success or failure of the believers. Many religions of antiquity no longer exist because of the military collapse of the states that once patronized and sustained them. Few today still worship the gods of Rome, Greece or ancient Egypt, in large part because of the collapse of those ancient empires, with foreign domination bringing the eventual supremacy of foreign gods.
Sometimes, the success or failure of a religion hung in the balance between victory and defeat in a single battle. In the great siege of Jerusalem by the Assyrian king Sennacherib in 701 B.C., for example, King Hezekiah heroically resisted the Assyrians following the prophecies of Isaiah (see 2 Kings 18-19).
Hezekiah's firm military resistance, accompanied by a plague in the Assyrian camp, resulted in the salvation of Jerusalem, and hence, in the continued existence of Judaism as a religion. If the kingdom of Judah had fallen to the Assyrians — as had occurred to their sister kingdom, Israel, in 721 B.C. — it is likely that Judaism would not have survived. And hence Christianity and Islam would never have existed.
If the recently converted Christian emperor Constantine had been defeated at the battle of Milvian Bridge in A.D. 312 by his pagan rival Maxentius, it is quite likely that Christianity would not have become the state religion of the Roman Empire — or at least not in the form that it did.
Muhammad, the founder of Islam, was wounded at the battle of Uhud in A.D. 625; if he had been killed, instead, nascent Islam would undoubtedly have ceased to exist.
In Tibet, the military backing of the recently converted Dzungar Mongol warriors in the 17th century helped to establish Lobsang Gyatso, the fifth Dalai Lama, as the supreme ruler of all Tibet.
The amazing conquest of the Aztec empire by the Spanish conquistadors between 1519 and 1521 represented not only the triumph of Spanish imperialism, but the victory of Catholicism over Aztec paganism.
Earlier, the Spanish conquest of Iberia in 1492 ultimately resulted in the expulsion of hundreds of thousands of Jews and Muslims from the region of modern Spain. In the second century A.D., the conquests of northern India, western Iran, Afghanistan and parts of Central Asia by Kanishka, the great Iranian Buddhist king of the Kushan empire, facilitated the spread of Buddhism not only throughout his empire but along the Silk Road into China, as well.
Few today remember that Afghanistan was a predominantly Buddhist country for nearly a thousand years, from the second century B.C. through the Arab conquests in the seventh century A.D.
On other occasions, long-term military conquests could bring significant religious change. Alexander the Great's conquest of the Persian empire in the fourth century B.C. facilitated the spread of Hellenism — Greek language, culture, politics, science and religion. Hence, statues of Greek gods, and of Alexander as a god, have been found from Egypt to Afghanistan.
When Arab Muslim armies conquered most of the Middle East and North Africa in the seventh century, many of the conquered peoples saw the Arabs' unending string of military victories as clear evidence of the reality and power of their one God, Allah. Rapid conversions ensued in many conquered areas, and Islam is one of the most significant religions in the world today.
Thus, although religion today is rightly understood in the nexus of theology, ethics, belief and practices, religions always exist in a specific historical time, space and cultural context. Just as victory or defeat in war can radically transform political and cultural boundaries, the results of war have always had significant impact on the rise, spread, dominance or decay of religions.