This requires you to reach 100% popularity in a single town. To increase your popularity you need to keep a steady supply of needed goods and be sure not to buy so much that you leave the town without enough food or resources, as this will decrease your popularity. You can also boost your popularity doing missions for the town’s administrator or governor. Once you reach 100% the achievement will unlock.
This will come naturally as you progress through the Trader campaign when you start building and trading in Cayman.