Cotton! Yes, that’s where it all begins.
The production and processing of cotton is pivotal to sustain the drive of the fashion industry, and as items get cheaper and cheaper so too does the price of cotton. Cotton production has a checkered history and we can't expect it to get any better until the drive for fair production standards and living wages become a priority for all factories purchasing cotton for garment production and the demand for cheaper and faster fashion relents.
Uzbekistan has a long history of forced labour for the purposes of cheap cotton production, this video by an organisation called Anti-slavery highlights the current situation and the need for action.
Check out http://www.antislavery.org/english/ for more info.