I've heard it claimed several times that the Crusades were actually an attempt to remove a violent class of warriors from Europe by giving something to do besides war with each other (it was originally
Steven Runciman's idea?). How is that claim regarded these days?
aren't those the 2nd sons , set to inherit nothing ? Was very "available" a few years back here in Turkey as the country was becoming New Turkey and everything of Western origins to become suspect .
It's associated with the "second sons" idea, yes. They're not exactly the same thing, but they're related.
The second sons claim is that, due to the nature of primogeniture, all but the first son of a family would be set to inherit either nothing or very little. Therefore, those second sons would have to find some other way to make their fame and fortune other than inheritance, and they found it in military adventurism, adventurism that was supposedly, in the Crusading era, redirected overseas in the general direction of non-Catholics. The claim was not Runciman's - it's about a hundred years older - and is clearly not borne out by the evidence. Going on Crusade was often a family affair, and when single sons did it they were usually first sons rather than second sons. A cursory survey of the leaders of the First Crusade - mostly powerful landed nobles in their own right - shows this fairly clearly, but thorough analysis of the individuals known to have gone on Crusade through various other forms of data bears it out. There are other aspects to arguing against the thesis. For example, crusading was generally very expensive, not a matter for poor freebooters and adventurers. The second sons claim is, therefore, not held in much repute nowadays.
Runciman's history is slightly different (and it would be deeply unfair to try to summarize it here, but I will try). He was a master of the literary sources, and generally sympathetic to the non-Catholic participants in the wars. He viewed Christianity as fundamentally a religion of peace that was horribly perverted by the call to holy war. His strongest complaint was against the Fourth Crusade, which pitted Catholic Crusaders against Orthodox Greeks and as such, he believed, was the worst kind of crime. (His argument in part was based on the premise that attacking the Byzantine Empire destroyed the West's bastion against Islam and, in particular, "the Turk".) For Runciman, one of the motive factors for holy war was a desire to get rid of that violent class of warriors, yes, and I believe he explicitly connected that desire to the so-called "peace of God" movement in medieval Europe. The "peace of God" was an attempt to delegitimize violence toward fellow countrymen and Christians; in Runciman's view, it was impossible to eradicate this violence, so Catholic leaders cynically redirected it overseas.
I would say that many modern scholars would downplay that explanation. The "peace of God" was important for the history of the Crusades, but mostly in terms of demonstrating a relatively new and surprising willingness on the part of secular military leaders to listen to the Church at all. There are serious questions about how widespread the peace actually was, and how long it lasted, and whether it had an identifiable ideological connection to the reformist papacy that formulated a theory of just war from the 1060s onward.
Runciman believed that a theory of just war was fundamentally incompatible with the Christian religion (and that, therefore, any declarations to the contrary must have been motivated by other factors), but the medieval papacy appears to have disagreed. Whether these medieval Catholics were right or wrong doesn't really matter next to the fact that they
believed they were right. They weren't just spouting propaganda. I would say that, while it's certainly possible to identify other individual motives (venality, violence, and hatred cannot be fully separated from any war), by and large Christians went on Crusade because they really believed that by doing so they were being better Christians.