The First Crusade happened because of a confluence of geopolitics with Islamic invasions pushing Alexios Komnenos to talk to Pope Urban II, a religious revival that accompanied the preaching of men like Peter the Hermit and Urban's tour across France, and the incentive of new lands, new kingdoms, new wealth and papal indulgence for peasants, knights and lords. The leaders became organizational centers, with men like Bohemond and Baldwin I holding the spirits of their men together and making shrewd campaign moves in between nearly-catastrophic losses. Thousands of men speaking a half dozen different languages managed to coordinate a land crossing through France, the Balkans and Anatolia to head to The Levant and stay organized in a hostile environment inimical to what they were used to.
Glossing over Bohemond's shenanigans and Alexios being a based chad, they then actually had to fight their way down the coast. The armies would have died in the desert dozens of times if Alexios hadn't sent them shipments of supplies and new Crusaders. The army would have died in Antioch if a wannabe prophet hadn't lied about finding the Holy Lance. The army would have died at the gates of Jerusalem if someone hadn't told them how to beat Greek fire. Then the absolute mad lads had to hold onto some of the most hotly-contested territory in the Mediterranean while under attack from every side but the sea, including by their former ally Alexios.
Imagine trying to do any of that shit today. A leader of any nation, especially one comparable in power to the Byzantine Empire, coordinating with former members of foreign governments to form a free army that crosses over a dozen international borders. That free army is made up of career soldiers leading regiments of amateurs, training them on the road and organizing them into companies, all of whom have left their homes behind to earn war spoils or to take property for themselves in the Levant. Then you give them guns, artillery, aircraft, food, water, vehicles, replacements and components, to fight Egypt, Iran and Iraq all at once and win.
Imagine armies of Christians carrying rifles and crewing tanks seeing signs in the sky, hearing prophets proclaim that they've rediscovered holy relics, starving, eating grass and leather, enduring lethal disease, getting dehydrated from supply issues, and still retaking those cities anyway. Reinforcement, engagement, siege, capture, repeat, all the way down to Jerusalem. Then beseiging Jerusalem, winning despite being shelled to fuck and attacked with napalm, and winning AGAIN. Imagine the news after the Crusade force sweeps in, killing every single Muslim they can, taking their houses for themselves, cutting people open because they swallowed coins and engagement rings, and forcing the remaining living population to drag the corpses outside to be burned. All this in the name of protecting Christians from being raped, murdered and enslaved by Islam.
It's practically unimaginable to the modern mind. What kind of men would dare such devotion, especially while operating under constant social excoriation from social media? Would Christ even want us to go through that? I don't think it'll ever happen again.