Learn Icelandic: Þrátt fyrir að mótlætið var endalaust gáfust þau ekki upp. - Despite the fact that the adversity was endless, they did not give up.

Unlike þó að (even though), which usually forces the subjunctive mood, þrátt fyrir að often takes the indicative mood when stating an established, real fact. Since the endless adversity actually happened, the indicative var is perfectly natural here.

Why does the main verb gáfust come right after the subordinate clause?

This is the V2 (verb-second) rule in action. The entire subordinate clause (Þrátt fyrir að mótlætið var endalaust) counts as the first block of information. Therefore, the main verb gáfust must immediately follow it to take the second position in the sentence.

Why is the middle voice form gáfust used here instead of the active voice?

The verb for quitting or surrendering is gefast upp, which requires the -st ending (middle voice). If you used the active voice gáfu upp, it would mean giving up a specific item or piece of information, rather than yielding to adversity.

How does the noun mótlætið dictate the form of the adjective endalaust?

The noun mótlæti (adversity) is neuter. Because it is the subject of the subordinate clause, the adjective describing it must also be in the neuter singular nominative form, which is why we add the -t ending to get endalaust.