These suggestions were followed by the menace of overt acts which, if committed, would have had very serious results. In 1851, the British and French governments let it be known that instructions had been given to their naval commanders to increase their forces in the waters adjacent to Cuba, and to exercise guardianship over the shores of that island to prevent the landing of any more filibustering expeditions from the United States or elsewhere, such as those of Lopez. It does not appear that this was done at the request of Spain. It was probably an entirely gratuitous performance intended partly to ingratiate the Spanish government, and partly to prevent the possibility of the seizure by the United States of Cuba. But it was certainly a most unwarrantable meddling in affairs which concerned only the United States and Spain. No possible justification for it could be found in international law. In the absence of a state of war, it was intolerable that vessels under the United States flag should be subjected to search upon the high seas, while, when they reached Cuban territorial waters, no other power than Spain had any right to interfere with them. Daniel Webster was at that time ill and unable to perform the duties of his office, but J. J. Crittenden, who was acting as Secretary of State, made a forcible protest against any such action by Great Britain and France, and gave warning in the plainest terms that it would not be tolerated by the United States, and that any interference with American shipping between the United States and Cuba would be resented in the most vigorous manner. The result was that the British and French navies refrained from the contemplated meddling. Following this, however, Spain made a direct appeal to the British government for protection against American aggression. The request was not so much for immediate military intervention as for securing treaty guarantees. The British government was in a receptive mood, and, in consequence, in April, 1852, it proposed to the United States that that country should join it and France in a tripartite convention, guaranteeing to Spain continued and unmolested possession of Cuba, and explicitly renouncing any designs of their own for the acquisition of that island. It may be recalled that a similar proposal had been made by Great Britain and France in 1825, and that its acceptance had been favored by no less an American statesman than Thomas Jefferson, although, under the wiser counsels of John Quincy Adams, it had been rejected.