For one thing, if the Dominican Republic is your topic, it is far too broad for an essay. So, you need to narrow the topic by deciding upon about which aspect of the Dominican Republic you wish to write. For instance, a unique feature of this nation is that it is one of two Caribbean islands that are occupied by two countries. For, the western third of the island is occupied by Haiti.
If you decide to examine this aspect, you can discuss the problems that arise from two different cultures. Or, if you wish to write about another aspect, you can write about the Dominican Republic's having become the Caribbean's largest tourist destination.
So, do the research on this country and find an aspect that appeals to you and write about this aspect. Remember that you must narrow the topic to one idea in a thesis statement. Your thesis contains three major points with your opinion. If, for example, you decide to explore the tourism of the Dominican Republican, then limit this idea to three major aspects of tourism.
For more helpful tips on writing, see the sites listed below.
If you can clarify your question a bit further, I can give you a more direct and complete answer here. Dominican Republic is a topic, but what aspect of the country do they want you to write about? Is it a profile paper? Current events? Economic analysis? Physical and human geography? If you specify I'll edit this answer to help you with a thesis.
In the meantime, here's a link to the CIA website's World Factbook page for the Dominican Republic, which covers a lot fo the basic information.