They attacked Christian dukedoms and principalities in the name of evangelization, falsely accusing them of being pagan when they in fact were not. Those they defeated, they also enslaved, even though they were Christian.
When recruiting troops in the West for their war against Poland in the 15th century, they would falsely tell recruits that it was for a crusade against a pagan kingdom, even though the Polish kingdom had been Christian since the 10th century.
All in all, they were a horrible, evil group of people who committed unspeakable atrocities in the name of Christ.
It is a pity King Jagelo of Poland did not completely wipe them out after winning his war against them. Instead, he signed a treaty with them and let them become vassals of the Polish crown. That was a big mistake.
> It is a pity...
Please emotionalize somewhere else. This happened 600 years ago.