As nation states and technology developed, war became more frequent and more bloody, culminating in the gory 20th century. However, since then wars between nation-states, especially among the major powers, have decreased. The first reason for fewer wars is that WWI and WWII cost way more than any benefits they produced – showing everyone that wars are simply not cost-effective. Similarly, the result of all the death and destruction of the Korean War and the Iran/Iraq war was restoration of the original borders. And the U.S. spent far more on its Iraq war than the value of oil that has been pumped.
Another factor that discourages great-power war is the advent of nuclear weapons, which can result in terrifying mutual catastrophe. So, the nuclear states - the major powers - have avoided war with each other.
In addition, the moral view of war has totally changed from the days when kings and generals thought of war as glorious proof of their courage and vigor. The mass carnage of WWI, WWII, Korea, Vietnam, Iran-Iraq, Congo, Yemen, etc. has made the uselessness, futility and immorality of war crystal clear to most people.
Another factor is that the key elements in economic growth and power today are not only natural resources and military power, but ‘soft power’ factors such as technology, a well-educated population and good governance. If there is a war, international trade will be disrupted, factories, schools, research labs and infrastructure will be destroyed, the best educated people will leave and the country will be misruled by warlords (e.g., Yugoslavia, Afghanistan, Somalia). It can take decades for an economy to recover from a war. War is just not good business for most people - only arms dealers and military leaders benefit.
Finally, the since the end of the Cold War, the U.S. and USSR have reduced supporting proxy wars, while international peacemaking and negotiations have increased, helping reduce or end conflicts in Northern Ireland, Liberia, Ivory Coast, Congo, etc.
Civil War, Irregular War, Asymmetric War and Terrorism - the Weapons of the Weak
Today, most wars are unconventional, irregular or civil wars. This has been a change in the nature of war - from large-scale conflicts conducted by nation-states to what is sometimes known as asymmetric warfare. For instance, there were two large civil wars (Yugoslavia and Rwanda) in the early 1990s, and today there are large civil wars in Congo, Syria, Somalia, Yemen and Southern Sudan. Two-thirds of the wars since WWII were civil wars.
Weaker groups see the impossibility of winning conventional conflicts against major powers or their own governments and so have turned instead to guerrilla war, terrorism and other cheap, unconventional methods. Stealing a truck and running people over costs nothing. Making a roadside bomb or outfitting a loner shooter or a suicide bomber only costs a few hundred dollars. Including extensive dry runs, the 9/11 attack only cost about $300,000 and caused 3,000 deaths and tens of billions in damages. In June 2019, Iran shot down a U.S., Global Hawk drone that cost $130 million using an indigenous missile that cost about $100,000.
Nation-states have also carried out terror against their own people (Asad’s Syria, Duterte’s Philippines, Stalin’s Russia, Hitler’s Germany, Mao’s China, South Africa under apartheid, Iran under both the Shah and the ayatollahs, and military juntas in Greece, Argentina and Brazil). In fact, most casualties in modern times were the result of governments killing their own people, what Rudoph Rummel termed democide.
Some governments (Iran, Syria, Sudan, Libya, North Korea) support terror and other irregular warfare against other countries. Russia took over Crimea and Eastern Ukraine, but instead of formally invading, it sent special forces without any insignia (“little green men”) and supported local militias that want to break off and join with Russia. (One of those groups used Russian-supplied missiles to shoot down an innocent Malaysian Airlines plane that was passing overhead.) Nation states also support different sides in civil wars in other countries. For instance, Iran uses proxies and its own Quds Force in Lebanon, Iraq, Syria and Yemen to engage in hybrid war, i.e., a mixture of conventional and asymmetric tactics.
Revolutionaries have long used guerrilla and terror tactics. George Washington learned to avoid direct confrontation with the British unless he had many more troops, instead using surprise attacks and shooting from behind trees and rocks. (The British thought this was cowardly.) The Spanish used ‘guerrilla’ war (small war – avoiding direct confrontation) against Napoleon. Mao Ze Dong used guerrilla war to defeat the Chinese Nationalist government and Japanese invaders in the 1930s and 40s. (“The enemy advances, we retreat; the enemy camps, we harass; the enemy tires, we attack; the enemy retreats, we pursue.”) The Algerians used guerrilla war and terror bombs to drive out the powerful French military in the 1950s. The Vietnamese used guerrilla war and terror bombs first to drive out the French and then the Americans from the 1950s to the 1970s. Guerrillas pushed the Portuguese out of Mozambique and Angola in 1975. The mujahedeen guerrillas pushed the Russians out of Afghanistan in the 1980s. Hizbollah’s roadside bombs and guerrillas pushed the Israelis out of Lebanon in 2008. Today, the Afghan and Iraqi rebels use hybrid war - roadside bombs, car bombs, suicide bombs, assassinations and snipers in addition to conventional ambushes and infantry attacks assisted by mortars and rocket-propelled grenades (poor man’s artillery). In Iraq, they disabled $5 million Abrams supertanks by firing $100 RPGs up the big exhaust pipes. The U.S. had to put protective grates over the exhausts.
Asymmetric war and terrorism are the weapons of the weak, using attacks against civilians and government to gain attention and try to advance a political agenda. Sometimes it is sponsored by nation-states (Iran, North Korea), sometimes by political or religious movements (Hamas, Hizbollah, Islamic State). The problem with fighting terrorist organizations is that often they have no homeland to counterattack, so that deterrence is ineffective. They must be incrementally rolled up, cell by cell, individual by individual. Terrorist groups may be ethno-nationalist (the IRA in Ireland, the ETA Basques, the PKK Kurds, the LTTE Tamil Tigers), religious/political (Al Qaeda, IS, Hamas, Hizbollah), or mixed (Columbia’s narco-leftist FARC). Good intelligence and police work, combined with military operations, have defeated many of these groups.
Osama Bin Laden saw how the U.S. military quickly defeated Saddam Hussein’s army, the 4th largest in the world, in two regular wars, so like Mao Ze Dong before him, he wrote in his fatwas that since the United States military is so powerful, it is necessary to use other methods. Similarly, in 1999 two Chinese analysts wrote in Unrestricted Warfare that in fighting a great power, guerrilla warfare, terrorism, propaganda, cyberwar and other means must be used. (Examples include Russian Internet attacks on the U.S. Democratic Party and the Estonian and Georgian governments, and Chinese hacks against U.S. companies and government agencies.) The U.S. electrical grid, railroads and other infrastructure and industries are highly vulnerable to hacking and both the Chinese and the Russians have apparently inserted Trojan Horses to disrupt them if there ever is a conflict. Not to mention financial pressure from China’s holding over $1 trillion in U.S. Treasury bills. Similarly, under the Gerasimov Doctrine of information warfare, Russia has used ‘active measures,’ including ‘compromat’ (smears against Western leaders) and used bots to send out millions of tweets and fake news stories to interfere in elections and cause chaos and division in Ukraine, Britain, France, Italy, the U.S. and many other countries.
These are all forms of what the military calls irregular, asymmetric or fourth generation warfare, i.e. which uses different means than the enemy’s strength. The U.S. “surge” in Iraq did not succeed in countering terrorism because it sent extra troops, but because it changed tactics to counter asymmetric methods. One way was by forging alliances with local leaders and developing local contacts by stationing small units within communities - counter insurgency (COIN). Another way was by conducting constant special forces raids to gather intelligence and capture rebel leaders - counter terror (CT).