Is extra history correct about the cause of the crusade?

I happen to be familiar with both videos so here we go. Both have their flaws for different reasons.

Extra History is not trying to be a comprehensive history of the crusades. It's format is to present episodes of history in 6 episodes, each 8 minutes long, which necessitates simplification. The channel 'Real Crusades History' is... well my interpretation is that it's quite a partisan presentation of events. They are very sympathetic to the Christian side of the story, and see the First Crusade as a 'clash of civilisations' which although applicable to later crusades, is not supported by the contemporary evidence for the First Crusade. The First Crusade has far murkier and complex origins.

The Extra History version puts Alexius I and Urban II, and their goals, at the centre of the First Crusade. I think that's is a valid perspective supported by contemporary evidence. The core of the 'Real Crusades History' video is that the First Crusade was a response to Muslim aggression, especially the aggression of the Seljuk Turks and their tyranny in the Middle East. Whilst the First Crusade was certainly prompted by the seemingly relentless advance of the Seljuk Turks, Extra History is right to point out that if the First Crusade was about Jerusalem being in Muslim hands and Christendom's issues with Muslims more generally, then it needs to be explained why they cared so much in 1095 and not earlier. After all, the papacy had been receiving pleas for help since the 1070s and done very little.

So the core question, it seems, is whether the Turks really were as bad as Urban II said they were. The answer is that they were in the 1070s, but had somewhat improved their conduct by the time of the First Crusade some 20 years later. Urban II's complaints about pilgrims being attacked, stripped and beaten, or murdered and their blood drained into baptismal fonts were, however, complete fabrications.

'Real Crusades History' draws on one main source, Aristakes Lastivertsi, an Armenian chronicler. His work, entitled About the Sufferings Visited Upon by Foreign Peoples Living Around Us, has a pretty obvious axe to grind. His complaint is basically 'why can't everyone just leave the Armenians alone' which, whilst a fair perspective given the state of Armenia at the end of the 11th century, presents a very slanted view of the enemies around him. He recounts in vivid detail the atrocities of the Seljuk army as it first arrived in eastern Anatolia, wrapped up in apocalyptic imagery lifted straight from the Bible. The leader of the Seljuks at that time was Alp Arslan who was indeed a tyrannical and violent man. Arab and Byzantine sources likewise recall the arrival of the Seljuk Turks as a horrific event. This is what the contemporary Islamic historian Sibt ibn al-Jawzi had to say about the Seljuk capture of Ani, Armenia's largest city, in 1064:

The dead bodies were so many that they blocked the streets; one could not go anywhere without stepping over them. And the number of prisoners was not less than 50,000 souls. I was determined to enter the city and see the destruction with my own eyes. I tried to find a street in which I would not have to walk over the corpses; but that was impossible.

Alp Arslan, having utterly crushed the Armenians, turned his attention to the Byzantine Empire and won an astounding victory at the Battle of Manzikurt in 1071. This prompted an envoy to the pope asking for aid, which was nearly given, but a rift between the Byzantine government and the papacy meant that the expedition was cancelled in 1074 and aid was not forthcoming. Alp Arslan died and was replaced by Malik-Shah I in 1072.

However, this material is difficult to use in support of Seljuk violence in the Holy Land because Armenia is not the Holy Land, and these events were a generation too early. It does at least tell us where some of Urban II's stories might have come from, but that's about it. Urban II does not directly mention Armenia in his speech, as far as we know, and the crusade certainly wasn't to save Armenia. Although the crusaders wrote at length about wanting to help eastern Christians, they meant the Christians of the Holy Land and cared very little about the Armenians. Malik-Shah I had very little interest in expanding west, and instead spent most of his reign in the northern part of his empire attacking Georgia (which he did with brutality, but not the same extent as Alp Arslan), and quarrelling with the Abbasid Caliphate, which he eventually triumphed over and brought Baghdad under Seljuk control.

By the time the Seljuk Turks had swept into the Holy Land, their leadership and their tactics in battle had changed. No longer relentless conquerors looking to sweep aside all in their way, they pivoted their strategy to better form an empire with a long term future. The empire was divided into areas such as the Sultanate of Rum, which continued to push west into Anatolia, and the Emirate of Damascus, which pushed into the Holy Land. But when Malik-Shah died in 1092 the empire fragmented into these fiefs. The plan to stabilise and give the empire a long term future by dividing it into semi-autonomous chunks was an utter failure. With the death of Malik-Shah, the Seljuk Empire went from the most terrifying entity the Middle East had seen in centuries, to an inept and flailing collection of principalities. The Sultanate of Rum, led by Kilij Arslan, had its act together, but most of the others were slowly falling apart. The area of the Holy Land was ruled by Tutush I, emir of Damascus and brother of Malik-Shah, but he died and the area was split between his sons Ridwan and Duqaq, based in Aleppo and Damascus respectively. They immediately turned on each other. They fought along the main road between the two cities, and neglected the other regions.

So as of 1092, Jerusalem and much of the Holy Land wasn't really ruled by anyone. There was conflict between Ilghazi ibn Artuq and his brother Sokmen over who got to govern Jerusalem, but this was such a minor thing it's barely mentioned in contemporary sources and they spent most of their time with Duqaq rather than actually governing the city. We know most of this from one Islamic local historian who was just trying to keep up with the political machinations of the Ridwan v. Duqaq situation.

This leaves us with an odd situation. If the First Crusade was, from Urban II's perspective, about saving the Christians of the Holy Land from the ravages of the Seljuk Turks, then 1095 doesn't make a whole lot of sense. It was the low point of Seljuk aggression, and a period when the empire was breaking up in a manner that Alexius I happily exploited with and without the crusaders. The state of Jerusalem was actually pretty good as of 1095; it and other cities in the area enjoyed de facto autonomy and the benefits that came with it. One of the great frustrations the crusaders faced was that many of these cities, which had mostly Christian populations, opposed them rather than flung open their gates. They'd been told the locals were crying out for liberation, but found the local Christians a mix of confused, welcoming, and outright hostile. The Ridwan v. Duqaq conflict no doubt had an adverse effect on the area, as all wars do, but as I said they both neglected Jerusalem and mostly left it to its own devices so it was somewhat shielded from all this.

Whilst simplified, it does present other factors that led to the First Crusade. Urban II and the reformist papacy were looking to curtail the violence of Europe's knights, or at least direct their violence in a manner more acceptable to Christianity. Urban II was also looking to rebuild the power of the papacy, which had been booted out of Rome by the Holy Roman Empire, and this was the opportunity to do it. Earlier that year, Urban had persuaded king William II of England to support him as the legitimate pope, and he had trailed the idea of indulgences and remission of sins in the wars in Iberia with some promising results. Alexius I did want help against the Sultanate of Rum which, although not the tyrannical oppressors Urban railed against, were still an aggressive military power with the potential to do serious damage to the Byzantine Empire and Alexius I. So when Byzantine envoys arrived in early 1095 asking the pope for aid against the Sultanate of Rum, all the pieces fell into place. Urban II had introduced the idea of indulgences, he had the momentum in the struggle against the Holy Roman Empire, he had rebuilt the exiled papacy's bureaucracy into a formidable propaganda machine, and here he had the casus belli to deploy these things in one great show of strength. Unsurprisingly, Urban II then used one of the crusading contingents to march on Rome and take it back from the Holy Roman Empire and seemed to lose interest after that.

This is all to say that when the Extra History video states that there was little if any evidence for the atrocities Urban II spoke of, it is oversimplifying but it's also essentially correct. By 1095 the Seljuk Empire wasn't the terrifying oppressor it used to be, and had not terrorised the Holy Land nor sought to impede pilgrimage. The early 1090s were no doubt a difficult time as the Seljuk Empire disintegrated, but not on the scale Urban portrayed. The atrocities that form the backbone of 'Real Crusades History' took place a generation beforehand and in a different place, which were not the focus of Urban's speech. That being said, crusaders believed these atrocities were real and continually happening, but Extra History's video writes mainly about Urban and his motivations which, although simplified, are I think fairly portrayed.