Marx saw the peasantry as a conservative and maybe even a reactionary force. This was based on his study of french history, where peasants caused Napoleon III to get into power. In many countries, the peasantry was the largest class, not the proletariat. For the proletariat, the revolutionary class, to take power, it would need to be the largest. This of course could be misinterpreted as an absurd position that peasants need to be killed, when what was actually meant was that the country would need to industrialize far enough to create a sizable proletariat.

Either way, history shows that an alliance of the proletariat and peasantry is capable of revolution.