Many Spanish colonies had gained their independence by the mid-1850s. In Puerto Rico, there were two groups: the loyalists, who were loyal to Spain, and the "independentistas", who advocated independence. In 1866, Dr. Ramón Emeterio Betances, Segundo Ruiz Belvis, and other independence advocates met in New York City where they founded the Revolutionary Committee of Puerto Rico. An outcome of this venture was a plan to send an armed expedition from the Dominican Republic to invade the island. Several revolutionary cells were formed in the western towns and cities of Puerto Rico. Two of the most important cells were at Mayagüez, led by Mathias Brugman and code-named "Capa Prieto" and at Lares, code-named "Centro Bravo" and headed by Manuel Rojas. "Centro Bravo" was the main center of operations and was located in the Rojas plantation of El Triunfo. Manuel Rojas was named "Commander of the Liberation Army" by Betances. Mariana Bracetti (sister-in-law of Manuel) was named "Leader of the Lares Revolutionary Council." Upon the request of Betances, Bracetti knitted the first flag of Puerto Rico also known as the revolutionary Flag of Lares ("Bandera de Lares").