The current Turkish campaign against the PKK and as a fig leaf against D'aesh repeats a hint already given by other entanglements in the chaotic MidEast.
Let's assume that U.S. and/or EU approval for the Turkish actions against the PKK was required. This assumption is basically the assumption that great powers still hold great power over small powers.
The Turkish government exploited the U.S. interest in hurting D'aesh (including use of Turkish air bases) to create a situation in which the combination of Turkish reignition of their pointless civil war against a faction of the Kurds (this time for domestic political power gaming) is tolerable because it's offered as a package with anti-D'aesh measures. The latter come at almost no expense for the Turkish government, and direct Turkish efforts against D'aesh were minimal and largely temporary. Still, the Turkish government packaged one evil with partisanship and thus recreated what we've seen a lot during the Cold War already, when Western powers backed many tyrants because they pledged to be "anti-communist": The Western great powers look away.
This shows how sometimes and maybe very often the "influence" of great power can only improve the world if said great power stays neutral instead of committed to hostilities to some ideology, bloc, country or organisation. They can be cynically played by small powers once they become committed and thus partisan.