Answer
Secession was a significant effect of Mella's leadership in Carlism. Mella's influence led to the formation of a breakaway faction within Carlism, known as the Mellistas. This faction sought to establish an independent Carlist state in the Basque Country and Navarre, separate from the larger Carlist movement. The Mellistas' secessionist aspirations ultimately weakened the Carlist cause and contributed to its eventual decline.