contrapusieran
Imperfecto de subjuntivo para el sujeto ellos/ellas/ustedes del verbo contraponer.

contraponer

Aparte de Finlandia, no existían parlamentos nacionales en el imperio a los que se contrapusieran los soviets: el nuevo gobierno provisional era una institución auto-designada, no electa, que perdió muchos apoyos precisamente por postergar sistemáticamente la convocatoria de la Asamblea Constituyente.
Apart from Finland, there were no existing national parliaments in the empire against which the soviets could be counterposed–the new Provisional Government was a self-appointed, unelected institution that lost much of its support precisely for constantly delaying the convocation of a Constituent Assembly.
Palabra del día
el petardo