Modernization of production in the agricultural sector is a critical driver of economic development. However, it can generate conflictual claims on previously uncontested land. This paper shows that the expansion of commercial farming induced by a market-oriented reform and technological innovation increased land conflict since the mid-1990s in Brazil. We find mechanisms involving the decline of economic opportunities for the rural poor: the reduction of informally accessible land for traditional farmers, the loss of employment for rural workers and the rise in land inequality. Moreover, suggestive evidence indicates that agricultural modernization strengthened the landless movement’s political incentive to engage in land disputes.