They didn't know the war will happen when Arjun married Subhdra, did they? Dury was never a contender for Subhadra
The question is, Did Krishna's son abduct Duryodhan's daughter before or after the dyut? There was no reason for war before Dyut, Was Laxmanaa way older than Abhimanyu to be abducted before Dyut?
Duryodhana would have killed to have an alliance with Krishna yet he is the one who captured Krishna's son and Krishna's brother had to pacify him into releasing Krishna's son, the incident doesn't really shows Duryodhan very fond of the idea of his daughter's marriage with Krishna's son
Why would Samba's father have an attachment with Kauravas? As you said samba, himself was present in pandava side, Duryodhan's daughter was with Krishna, Krishna's son didn't live with Duryodhan
Why didn't Krishna fight in the war? Why didn't his sons fight in war?
1. If Samba marrying Lakshmana can be brought in, then Suyodhana being contender for Subhadra can also be brought in because neither episode is from MBh. What is good for the gander is good for the goose.
2. I believe it was you who stated the episode was before war. Well then, you should provide citation.
3. Suyodhana asking for Krishna's help is part of MBh canon. The Kauravas captured Samba AFTER he kidnapped Lakshmana, not before. Which makes Suyodhana a good father. That doesn't mean he had anything against Krishna. Also, Krishna didn't send Balram. Krishna didn't bother to go free Samba at all. Balram did that all on his own.
And like I said, since we are using non MBh texts to malign Krishna, we can also use the part where Krishna cursed Samba for sleeping with his stepmothers.
In MBh proper, Samba is clearly stated to be a troublemaker what with him insulting the rishis.
Doubt any alliance Krishna planned would have been through Samba.
Also, Suyodhana goes to ask for Krishna's help apparently in spite of all this.
4. It's become fashionable in recent days to claim Krishna didn't risk himself.
I would recommend you check how many times Krishna was shot at by Bheeshma, Karna, and others. Would also recommend you check how many times he begged Yudhishtira to let him take up weapons. Krishna definitely wasn't keeping himself safe.
In addition, Pradyumna is mentioned as Yudhishtira's bodyguard during Jayadrath vadh. Which means he wasn't fighting, but he was very much at risk.
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