Washington saw in the Kurdish militias known as the People’s Protection Units, or YPG, an effective force against Islamic State. It poured training and weapons into the YPG, putting it at the center of Arab and Kurdish factions, known collectively as the Syrian Democratic Forces. It gave them the necessary air support to beat back the jihadis and built them into a force numbering 60,000 to 75,000 fighters, according to estimates.
Source: latimes.com – Los Angeles Times