Vladimir Putin has defended his annexation of Crimea as a necessary measure to protect Russian-speakers from the supposed "bandits" and "extremists" in Ukraine's new government. But Western leaders fear this pretext could also be used to justify an invasion of other areas of Ukraine with large Russian-speaking minorities, particularly the eastern regions of Kharkiv, Donetsk and Luhansk. Putin's new doctrine might even extend to incorporating the Russian-speaking region of Transdniester in Moldova, on the far side of Ukraine.