Square Enix announced world merger plans
for Final Fantasy XIV
last month, but player feedback prompted the team to reassess their plans
. Those plans have now been finalized and the world merger will take place later this month. Starting today as part of that process, players can put in their world transfer applications for one of the various destination worlds. The transfer application period is open through March 19th and the transfers will be carried out during maintenance on March 27th.
Be sure to get any characters that you may have signed up before the merger to ensure that you land on a world of your choice.
Source: Final Fantasy XIV World Merger Announcement