What are the other civilizations of your world like?

I will only talk about those for which I have fleshed out enough to answer this question.

• Høysted: These is a region just north of Tsevav inhabited by many culturally similar tribes though they have recently fell under the vassalage of the Mayura Imperium after a bloody war but still retain autonomy due to their homeland being too difficult and fierce for the Mayuras to directly govern. They don't look kindly upon foreigners, some of them have internal rivalries as well which is also one of the causes why the Mayuras were able to defeat them. In any case, they don't have any "illusions" of non-violence like their southern neighbors and will usually easily execute POWs but they wouldn't do so immediately since it is more profitable to just ransom them out later on, they may also torture high level POWs for information and even execute to make an example of them. Though for them torturing or killing people just for the sake of doing so isn't looked that kindly upon and may be perceived as sadistic but that really depends from instance to instance. Sometimes POWs are even kindly treated if they happen to be from tribes with which they don't have that much of a bone with (e.g: allied tribes of their rivals) but usually if foreigners invade them like the Mayuras, they would deal with them absolutely ruthlessly. Also to be noted is that they do not believe in slavery since loyalty is a very valued virtue among and they believe a slave can never be loyal even though they do not contacts with places which indulge in slavery.

• Mayura Imperium: East of Tsevav across the great Shaone Delta lies a vast Empire stretching leagues after leagues ruled over by the great Mayura Dynasty. The military force of the Empire is a force to reckon with and is known to have decimated opponents, razed settlements (which includes mass rape, murder and looting) to the ground, and indulged in mass execution of POWs since they do not really have the need to ransom out for "petty trinkets" though they still do keep high level POWs to be used during signing peace treaties and mid level POWs are sometimes tortured for execution. Unlike the people of Høysted, the citizens (as they are never really anywhere close to the battlefield unlike the people of Høysted) arn't very aware of everything the army does and are only aware of their conquests and therefore have a glorified opinion of them.

• Kasurasa: To the South of the lands of Tsevav lies a vast desert but in middle of which lies to great Oasis one of which is linked to group of mountains on which some occasional rainfall does occur. In this region live the Kasurasa peoples, they are a group of semi-united tribes people who are experts in living in the desert, and do not have much resources to fare, therefore even if they take POWs they usually just keep them for short whiles and would just let them starve to death and if they cause to much trouble will kill them, though they do try to ransom them out and torture for information from time to time, in fact they may just free the POWs after getting what they want in the latter case.

• Jalma cai: To even more South of the Kasurasa lie the settlements of Jalma cai living around one single Oasis which is supplies by an underground freshwater river which also supplies the Kasurasa's oasis FYI. They dominate and regularly patrol important trade routes in the desert which act as their main source of income since their oasis is the only thing that connects the lands much to the South to the lands of the North (like Tsevav, Høysted, etc). They usually do not come into conflict with other people due to their isolated (yet connected) situation, so in case of minor skirmishes POWs are usually not taken and even they are taken it is for ransoming or information in which case they may be tortured but that is a rare instance since they have founded non-violent methods (like friendliness with a dose of fear) to be more useful for information gathering. Sometimes small conflicts also arise among the settlements in which case even if POWs are taken they will never be harmed as it invoke hatred for that particular settlement.

• Firadi: These are a nomadic group of people who are migrating out of their homeland and have already destroyed countless civilizations in their path, they have ravaged and destroyed many great cities, decimated the people by some selling them off as slaves and keeping some as slaves while raping and killing most of the rest of the people. I guess you can understand what their opinions of POWs are. But in any case, they have come into contact with Tsevav and destroyed everything South of the great Zokwdej river which flows through the middle of Tsevav is basically the lifeline of the region without which the region would be desert much like everything south of it. Now the people of Tsevav have been horrified by what they have inflicted on them even though a lot of them were timely evacuated after they got reports of what the Firadi were doing to another Kingdom south east of where they lie.

Is the Tsevav religion's concept of non-violence a response in any way to an opposing philosophy?

Not really, it has very ancient philosophical roots all of which stems from the belief that at the beginning of time all Sentient Souls were one and that one Soul itself is the cause of time and has created the rest of the world, therefore it is against the natural order for a part of the Soul in one being to harm another or else the Soul gets corrupted and suffers greatly after death and is unable to enter another new being after death for a very long time during which in its confusion, fear, rage, pain, etc may try to attack and enter other Sentient being causing misfortune, diseases, etc therefore the persistence of such corrupted Souls is harmful overall to society as well.