The Merengue has existed since the early years of the Dominican Republic around the time of the Spanish-American War (1898,) as well as in Haiti and was written about in the mid 1800s. The dance comes from the Upa Music (Urpa Dance) of Havana around 1840 which featured a part called "Méringue."
Colonel Alfonseca is reported with developing the Merengue and was supposedly created from a great Talanquera Battle (this is a myth). The Merengue is sometimes called the "Palm Beach One Step" or "Pambiche" (1916). A slower and fewer syncopated version was being called the "Jaun Ester" in Puerto Plata, while later being called the 'Pambiche'. The Merengue has roots in the Spanish "Jaleo."
The original dance was fast & agitated, while the newer (1950's & up) ballroom version being much slower and uses more hip movements. The Merengue was not introduced to the United States till about 1950 and had seen some acceptance and popularity. (Craze Magazine  reported that "the Fred Astaire dance studios were teaching the 'New' Haitian Merengue ?).
There are two folk stories as to the style of the dance.
1) Slaves, who were chained together by the ankles would use this "walking style" as they cut sugar cane to the beat of the drums (this has merit).
2) A great hero, (sometimes said a King or General) was wounded in action, and upon his return a great party was thrown in his honor. This hero/king loved to dance and tried to dance at the party but was not able with his wounded leg, the best he could do was limp and drag his wounded leg through the dance, so the dancers feeling sorry for him and not wanting to offend, limped and dragged one foot to the beat just as he did (popular story but sounds fictional.)
The basic step is just a walk ie: 1-2,1-2 etcetera, just walk in a marching type walk to each beat of music. There are many patterns that can be done in the Merengue however today it has become almost Salsa-ish with sometimes a hint of Lambada and freaking. The "merengue confection" used in pies and such (deserts) has been said to be the source of the name on occasion.
More To Come!