The trade in women is in
essence a form of
slavery.
Women from poor countries are offered nice jobs in rich countries, as a waitress or a nanny. They have to pay a huge amount of money for the journey and as a fee for the person who has arranged the job. Sometimes they pay beforehand, sometimes they promise to pay with the wages they will earn in their new job.
On arrival in the new country their passports are taken away (if they haven't been already) and the nice job turns out to be a job in prostitution. With no papers, no money, no residence permit, a enormous debt to the 'trader' and usually no knowledge of the local language, these women have no choice but to do what they are told.