Question

Did the idea of manifest destiny actually cause events, such as the political support for territorial expansion, or simply justify actions taken for other reasons?

Answer 1

I think that the idea of Manifest Destiny of the US caused actions to be taken to oppose any signs of political or economic independence in its supposed 'back yard' in Latinamerica up to the more recent times. So such things as the support and fostering of the Contras by Reagan and the invasion of Panama by Bush were part and parcel of this policy. It is only now that many Latinamerican countries have insisted on having progressive governments that the US cannot just have carte blanche in organizations like the OAS and had to finally recognize the legitimate existence of the socialist government in Cuba in order not to become more isolated in that part of the world.