 Complete the following phrase:  Meanwhile, the doctrine of manifest destiny had become increasingly sectionalized as the decade progressed. While there were still Northerners who believed the United States should dominate the continent, most were opposed to Cubas annexation, particularly as a slave state. Southern-backed filibusters, including Narciso López, had failed repeatedly since 1849 to 1851 to overthrow the colonial government despite considerable support among the Cuban people for independence, and a series of reforms on the island made Southerners apprehensive that slavery would be abolished. They believed that Cuba would be Africanized, as the majority of the population were slaves, and they had seen the Republic of Haiti 