The election marked a significant shift in Northern Ireland's politics, being the first election since Ireland's partition in 1921 in which unionist parties did not win a majority of seats, and the first time that unionist and nationalist parties received equal representation in the Assembly (39 members between Sinn Féin and the SDLP, 39 members between the DUP, UUP, and TUV). The DUP's loss of seats also prevents it from unilaterally using the petition of concern mechanism, which the party had controversially used to block measures such as the introduction of same-sex marriage to Northern Ireland.