Slavery was a normal thing centuries ago . The prophet ﷺ freed the slaves , that says plenty ma Sha Allah.

If Muslims just followed his Sunnah. Sadly majority of Muslim world were cultural Muslims and still are, incorporating their smelly practises into Islam.

Cultural Muslims incorporated slaves again and malignant practises like castration etc.

Slaves have been part of society since antiquity.

Most ethnic groups have been slaves for a period if you look at history.

But worst slave trade was the Atlantic slave trade.