The concept of “holy war” is most commonly expressed as a war justified on the grounds of religious differences. As typically understood, this concept is neither taught nor encouraged by the Bible. The ancient Israelites were never given a broad mandate to wage war on behalf of their faith, though they were given a specific time, place, and that which they were instructed to conquer. Jesus Christ explicitly contradicted the holy war concept through both His teachings and His example. The concept of “just war,” meaning justifiable war waged by a legitimate government, is not the same as a “holy war.”
Critics sometimes claim that holy war is encouraged in the Old Testament. However, the nation of Israel was given a mandate only to conquer the land of Canaan (Numbers 34:2). This command was for a specific place, time, and people, not an endorsement of religious warfare. Nor was the conquest of Canaan made on the basis of religion, in and of itself. On the contrary, God repeatedly stated that this conquest was due to the wickedness of the Canaanites, not the merit of Israel (Deuteronomy 9:4–6). Historically, this is exactly how the nation of Israel interpreted these commands. No attempts were made to conquer other lands or to expand that territory through combat.
Christians are strictly forbidden from using violence in an attempt to spread their faith. Christ directly told His disciples not to use violence to further His ministry (Matthew 26:52–54). He lived out a philosophy of peacemaking and taught others to do the same (Matthew 5:9–10). When arrested and facing death, Jesus clearly said that His kingdom was not earthly, so His disciples would not fight to protect Him (John 18:36). Christians expect persecution, not conquest, since Christ experienced the same (John 15:18–21). The example of the earliest believers was that of civil disobedience (Acts 5:25–29) and submission (Romans 13:4–5), never armed revolution or conquest. In fact, for the first three centuries of its existence, Christianity was effectively illegal, yet it spread throughout the Roman Empire.
The occurrence of “holy war,” historically speaking, is rare. Secular historians note that more than 90 percent of the wars fought in human history had no religious motivation. The remaining 7 percent of conflicts account for about 2 percent of all deaths in war. Islam accounts for more than half of these religious wars, despite existing for only about 1/3 of human history; in Islam’s first three centuries, its growth was fueled by armed conquest. If there’s any reason the concept of “holy war” exists, it’s fair to say that reason is Islam.
It’s also worth noting that atheistic regimes have resulted in untold millions of deaths, just in the last 100 years alone. Religious belief, historically, hasn’t been a major cause of conflict, while non-belief has enabled some of history’s worst atrocities.
The Bible maintains a strict emphasis on God’s righteousness and mankind’s fallibility. Jesus preached a message of peace and lived it out perfectly. His earliest followers did the same, and every attempt to justify “holy war” by nominal Christianity was met with opposition and dissent from within the church. Historically and theologically, “holy war” has never been a part of biblical Christianity.