Sinn Féin's victory takes NI one step closer to leaving the UK and reunifying with the Republic of Ireland. Though support for a united Ireland is still unclear, with only 37% of the population fully supporting it, the momentum is growing, and a referendum could be in sight.
Sinn Féin's victory doesn't mean that a united Ireland is on the horizon. The party was once the political appendage of the terrorist IRA, which wrought 30 years of havoc and misery, and its victory is certainly not good for the union. However, its overall support has only increased by around 1%. The true unionist majority has been obfuscated by the Single Transferable Vote system.
This election was a massive victory and important milestone for the Alliance party, whose success reflects a growing dissatisfaction with NI's traditional parties. The sectarian political rivalries that dominated the country's creation (and its politics since) have only hurt the Northern Irish people, and Alliance's gains indicate that voters want to move toward a more inclusive future.