The Peace of Cateau-Cambrésis ended a war that had become, if indeed it had not started as, ‘a race between spent horses’. It was a peace of exhaustion and it endured because for many years to come none of the states of western Europe felt strong enough to risk another general conflict. Yet although all were afraid to strike, some were still willing to wound. And the internal instability that afflicted all of them, bred of exhaustion and fevered by a crisis of conscience in religion, gave to any dissatisfied power repeated hopes of undermining the foundations upon which the 1559 settlement rested.

In that settlement the British Isles occupied a crucial position. For the treaties left one of the two outstandingly great powers of western Europe, France, hemmed in and all but encircled by the territories of the other, Spain. The dominions of Philip II of Spain ran almost all around France—from Spain itself through the Balearic islands, Sardinia, and Sicily to Naples, the Tuscan ports, Parma, and Milan, with dependent Corsica, Genoa, and Savoy-Piedmont linking on to Franche-Comté and the Netherlands. If the British Isles or at least England could be added to these, as during Mary Tudor's marriage to Philip II (1554–8), then the ring would be complete and virtually unbreakable. If, on the other hand, the French could control England as well as Scotland, then the sea route through the Channel and the Straits of Dover could be closed to the Spaniards.