Portuguese royal family was in America, and it was hence comparatively easy to rule in its name. But though political considerations dictated this step, it entailed also great military advantages. England having complete command of the sea, the French had to derive all supplies, except such food as the country afforded, from France, which was rendered very difficult by the guerillas. Spain, as a glance at the map shows, is greatly cut up by mountain chains: of these the Sierra de Guadarrama, south of the Douro basin, and the Sierra Morena, north of Andalusia, are serious barriers, though not impassable. The country between them is mostly barren, Andalusia (except parts of the east coast which do not enter into account) being the only very fertile region. Moreover the roads were few and bad. Hence it followed that large armies could not long hold together for want of subsistence, except in Andalusia; while even there a French army could not stay, if an enemy in the centre of Spain intercepted its supplies of ammunition, clothing, reinforcements, coming from France. Moreover in Portugal the English army, with an excellent harbour at Lisbon through which to draw its supplies and reinforcements, was on the flank of Spain. This was clearly the position most favourable[64] for dealing effective blows at the French power in Spain, taken as a whole. On these facts, added to the necessity of sparing his men to the utmost, for the English government could not supply large numbers, and by no means realised the importance of their opportunity, Wellington[65] based his general plan. He was convinced, as his Correspondence shows, that sooner or later the nations of Europe would combine to overthrow Napoleon's domination, and that meanwhile to keep alive resistance in the Peninsula would be a steady drain on his resources and would set an example to other nations. Hence his first object was to hold his ground in Portugal; his second was to trouble the French hold on Spain when opportunity offered. Finally he hoped, when pressure elsewhere compelled Napoleon to weaken his Spanish armies, to drive them altogether from the Peninsula. Thus the first, and by far the longest, portion of the war is defensive, the battles being only fought when a paramount object is to be gained; the latter portion is offensive.