In 1841 Aberdeen had sent Lord Ashburton to America with instructions to secure, if possible, a settlement of all matters in dispute.  Here was a genuine British effort to escape from national irritations.  But before the Treaty of 1842 was signed, even while it was in the earlier stages of negotiation, the British Government saw, with alarm, quite new questions arising, preventing, to its view, that harmonious relation with the United States the desire for which had led to the Ashburton mission.  This new development was the appearance of an American fever for territorial expansion, turning first toward Texas, but soon voiced as a “manifest destiny” which should carry American power and institutions to the Pacific and even into Central America.  Among these institutions was that of slavery, detested by the public of Great Britain, yet a delicate matter for governmental consideration since the great cotton manufacturing interests drew the bulk of their supplies of raw cotton from the slave-holding states of America.  If Texas, herself a cotton state, should join the United States, dependence upon slave-grown cotton would be intensified.  Also, Texas, once acquired, what was there to prevent further American exploitation, followed by slave expansion, into Mexico, where for long British influence had been dominant?

On the fate of Texas, therefore, centred for a time the whole British policy toward America.  Pakenham, the British minister to Mexico, urged a British pressure on Mexico to forgo her plans of reconquering Texas, and strong British efforts to encourage Texas in maintaining her independence.  His theory foreshadowed a powerful buffer Anglo-Saxon state, prohibiting American advance to the south-west, releasing Britain from dependence on American cotton, and ultimately, he hoped, leading Texas to abolish slavery, not yet so rooted as to be ineradicable.  This policy was approved by the British Government, Pakenham was sent to Washington to watch events, a charge, Elliot, was despatched to Texas, and from London lines were cast to draw France into the plan and to force the acquiescence of Mexico.

In this brief account of main lines of governmental contacts, it is unnecessary to recite the details of the diplomatic conflict, for such it became, with sharp antagonisms manifested on both sides.  The basic fact was that America was bent upon territorial expansion, and that Great Britain set herself to thwart this ambition.  But not to the point of war.  Aberdeen was so incautious at one moment as to propose to France and Mexico a triple guarantee of the independence of Texas, if that state would acquiesce, but when Pakenham notified him that in this case, Britain must clearly understand that war with America was not merely possible, but probable, Aberdeen hastened to withdraw the plan of guarantee, fortunately not yet approved by Mexico[9].