The Union of Arms (in Spanish Unión de Armas) was a political proposal, put forward by Gaspar de Guzmán, Count-Duke of Olivares for greater military co-operation between the constituent parts of the composite monarchy ruled by Philip IV of Spain.[1][2]
The plan was for each of the kingdoms ruled by Philip to contribute equitably to a fund from which 140,000 troops would be maintained for the defense of the monarchy.[3] The plan was "a thinly disguised attempt to integrate the fiscal institutions of the empire [that] prompted much opposition in the Indies."[4][5][6]
The division of contributions envisaged was:[7]
Although the proposal ultimately failed, it was an important factor in the growing mistrust of Castilian hegemony that led to the Reapers' War in Catalonia and the Portuguese Restoration War.