Learn Turkish: Bazıları düşmana meydan okurdu, yeter ki esaret bitse. - Some of them would defy the enemy, provided that the captivity ended.

The phrase yeter ki means provided that or as long as. When you pair it with a verb in the conditional tense, like bitse (were to end), it sets up a hypothetical or deeply desired condition. It essentially means if only it would end, then...

Why does düşman take the dative ending -a in düşmana meydan okurdu?

The phrase meydan okumak is an idiom meaning to defy or to challenge (literally to read the square). In Turkish, you issue a challenge to someone, so this idiom always requires the target to be in the dative case. Thus, düşman becomes düşmana.

Why is the main verb okurdu in the aorist past tense?

The aorist past formed by the aorist -ur plus the past copula -du translates to would do in English. It is often used for hypothetical situations. Here, it perfectly pairs with the hypothetical condition bitse to show what the subjects would be willing to do if their condition were met.

Could the yeter ki clause come at the beginning of the sentence instead?

Yes, word order is flexible here. You could easily say Yeter ki esaret bitse, bazıları düşmana meydan okurdu. Putting the yeter ki clause at the end, as this sentence does, adds a dramatic flair, making the condition feel like an intense emotional justification for their defiance.