 Complete the following phrase:  The main antagonists were, on a geographical level, Buenos Aires Province against the other provinces of modern Argentina, and on a political level, the Federal Party against the Unitarian Party. The central cause of the conflict was the excessive centralism advanced by Buenos Aires leaders and, for a long period, the monopoly on the use of the Port of Buenos Aires as the sole means for international commerce. Other participants at specific times included Uruguay, and the British and French empires, notably in the French blockade of the Río de la Plata of 1838 and in the 