I don't know much about the overseas leagues, but how do they compare? I see players in Turkey, Israel (which probably is in Turkey's league?), Russia, France, and China. Am I missing a Skandanavian team?
USA women's basketball is definitely the best in the world as the Olympic and WC teams have repeatedly proved and as most of the youth international teams have proved as well. PanAM and various other competitions that pit USA college players against foreign pros also point to the variance - while USA doesn't necessarily win the gold in those competitions they generally medal. In the US college scene we get occasional stars from foreign NT teams playing (Kia and others) USA NT teams generally include one senior or rookie pro as a 'twelfth man' to start learning the national game.
The foreign pro leagues all limit the number of foreign players allowed on the roster specifically to encourage the development of the 'local' players and to prevent a rich team from buying titles. The US players tend to be the stars, and in the lesser leagues US players who have failed to crack a W roster are still often the stars of the league - Kaili was a star in the Greek league, but has never been on a WNBA roster for example and Gardler played in Sweden for a few years but never got a training camp invite in the W.
The European leagues are set up very similarly to the soccer leagues - you have domestic (single country) and European competitions across the region for the better teams in each domestic league. Those extra competitions extend the seasons which is why a lot of players do not make it back for the W training camps.
Uconn and other US college teams can be very competitive against the league teams across Europe (especially since many of their foreign stars are playing in the W) while most of the W teams would wipe the floor with them. (USA college teams can be competitive against most National teams as well - many felt that the Uconn team would have done better against Canada in the last PanAms because they had trained together all year vs. the actual USA team that had been pulled together in a week and was led by the two Uconn stars while Canada was led by a third Uconn star.