Workers of the World Unite!... against Russia.

THIS is effective counterinsurgency.

MARIUPOL, Ukraine — Thousands of steelworkers fanned out on Thursday through the city of Mariupol, establishing control over the streets and banishing the pro-Kremlin militants who until recently had seemed to be consolidating their grip on power, dealing a setback to Russia and possibly reversing the momentum in eastern Ukraine.

By late Thursday, miners and steelworkers had deployed in at least five cities, including the regional capital, Donetsk. They had not, however, become the dominant force there that they were in Mariupol, the region’s second-largest city and the site last week of a bloody confrontation between Ukrainian troops and pro-Russian militants.