A third, constructivist, set of accounts stress the importance of the socially constructed nature of ethnic groups, drawing on Benedict Anderson's concept of the imagined community. Proponents of this account point to Rwanda as an example because the Tutsi/Hutu distinction was codified by the Belgian colonial power in the 1930s on the basis of cattle ownership, physical measurements and church records. Identity cards were issued on this basis, and these documents played a key role in the genocide of 1994.