The theory of common communications will become clear by taking an example. In our wars with France our communications with the Mediterranean, India, and America ran down from the Channel mouth past Finisterre and St. Vincent; and those of France, at least from her Atlantic ports, were identical for almost their entire distance. In our wars with the Dutch the identity was even closer. Even in the case of Spain, her great trade routes followed the same lines as our own for the greater part of their extent. Consequently the opening moves which we generally made to defend our trade by the occupation of those lines placed us in a position to attack our enemy's trade. The same situation arose even when our opening dispositions were designed as defence against home invasion or against attacks upon our colonies, for the positions our fleet had to take up to those ends always lay on or about the terminal and focal points of trade routes. Whether our immediate object were to bring the enemy's main fleets to action or to exercise economic pressure, it made but little difference. If the enemy were equally anxious to engage, it was at one of the terminal or focal areas we were almost certain to get contact. If he wished to avoid a decision, the best way to force him to action was to occupy his trade routes at the same vital points. Thus it comes about that, whereas on land the process of economic pressure, at least in the modern conception of war, should only begin after decisive victory, at sea it starts automatically from the first. Indeed such pressure may be the only means of forcing the decision we seek, as will appear more clearly when we come to deal with the other fundamental difference between land and sea warfare. Meanwhile we may note that at sea the use of economic pressure from the commencement is justified for two reasons. The first is, as we have seen, that it is an economy of means to use our defensive positions for attack when attack does not vitiate those positions, and it will not vitiate them if fleet cruisers operate with restraint. The second is, that interference with the enemy's trade has two aspects. It is not only a means of exerting the secondary economic pressure, it is also a primary means towards overthrowing the enemy's power of resistance. Wars are not decided exclusively by military and naval force. Finance is scarcely less important. When other things are equal, it is the longer purse that wins. It has even many times redressed an unfavourable balance of armed force and given victory to the physically weaker Power. Anything, therefore, which we are able to achieve towards crippling our enemy's finance is a direct step to his overthrow, and the most effective means we can employ to this end against a maritime State is to deny him the resources of seaborne trade.