Seward was the driving force behind American Civil War diplomacy, and much of his diplomacy was shaped by his imperial vision. For more than thirty-five years, Seward had extolled the promise, potential, and perpetuity of the American empire, and much of his Civil War diplomacy aimed at preserving, expanding, and ensuring the successful completion of that empire. Well before "manifest destiny" became the slogan of expansionists, Seward envisioned the expansion of the United States to include all of North America and quite likely South America and the islands of the Caribbean as well. He also spoke eloquently about the certain growth of the American economy and American overseas commerce and predicted that U.S. merchants, commercial agents, and diplomats would spread the principles and ideology of the American System around the world.
Seward's program required the centralization of American political power and the containment and eventual abolition of slavery in the United States. He promoted legislation to attract, Americanize, and assimilate immigrants, liberalize land policies, centralize banking and monetary programs, and fund internal improvements and federal money. He also believed that the gradual end of slavery and its replacement by free labor were essential for peaceful American expansion and the full growth of the American economy. Without the stain of slavery, he thought, Canada and Mexico would eagerly seek admission to the American commonwealth.
Slavery also gave excessive power to reactionary agrarian interests in the South. Containment of slavery to the states where it presently existed, gradual emancipation, and the reduction of Southern power in Congress, Seward believed, were made possible by the Republican victory of 1860, as was the restructuring of the American political economy and the expansion of the American territorial, commercial, and ideological empire. During the war years these programs were subordinated to the preservation of the Union, an end that Seward never questioned and a goal from which he never wavered.
Throughout the secession winter of 1860–1861 that followed Lincoln's election, Seward worked tirelessly to find a compromise or modus vivendi with those Southern leaders whose states had not left the Union. While Lincoln remained in Springfield, Illinois, preparing for his inauguration, Seward made a number of public speeches emphasizing the dangers, impracticality, and fruitlessness of secession. He opposed all actions that would close the door to the return of the disaffected states and tried to ensure that the Confederates received no encouragement, prospect of support, or tangible aid from overseas.
Although Seward did not assume office until Lincoln's inauguration on 4 March, he engaged European diplomats in Washington in private conversations that aimed, first, at assuring them that the secession effort would shortly collapse, and, second, warning Europe that the United States would not tolerate any foreign intervention in American or hemispheric affairs. Seward had predicted that if the United States became divided, European nations would sweep down upon the Americas to reestablish or expand their authority and influence. During the last weeks of March, these concerns appeared justified. Rumors were rife that Britain, France, and Spain were planning to intervene in Mexico, that Spain was about to recolonize the Dominican Republic, and that France was about to move back into Haiti. The first two had a basis in fact. The three European powers were discussing an intervention limited to collecting debts for their nationals who had invested in Mexican bonds, and the Dominican Republic, engaged in civil war, had asked Spain to return. Spain had agreed and dispatched a force from Cuba to reestablish a colonial government in Santo Domingo. The information that France was contemplating recolonizing Haiti was groundless. Seward chose to use this information both to reassert his waning authority in the cabinet and perhaps to take effective control of the Lincoln administration and generate an issue calculated to reunite the fractured nation.
On 1 April 1861, Seward sent Lincoln an extraordinary memo entitled "Some Thoughts for the President's Consideration." In the memo, Seward complained that the government lacked both a domestic and a foreign policy and was adrift. He recommended that Lincoln change the thrust of the American dispute from the question of slavery to that of union, and proposed that the United States seek "explanations" from France, Spain, Britain, and Russia for their plans and actions. (The Russian minister, Edouard de Stoeckl, had met with one of Davis's Confederate commissioners, and Northern newspapers reported that Russia was about to recognize the Confederacy.) If, Seward continued, France and Spain could not satisfactorily explain their intentions and their recent actions, Lincoln should convene Congress and ask for a declaration of war. In addition, Seward recommended sending agents to Canada and Latin America to promote independence and opposition to European interference in the New World. Finally, he suggested that this policy required energetic and constant attention and implied that if Lincoln was unwilling to provide leadership, Seward was willing to assume it himself.
Lincoln responded to Seward immediately, pointing out that he had already made it clear that his administration would not interfere with slavery in the states where it already existed and that the fundamental issue in the crisis was indeed the question of union. He also noted that recent dispatches which Seward had sent to American agents abroad clearly stated his administration's foreign policy. Finally, Lincoln said that he would continue to determine policy with the help of his entire cabinet.
Seward's chief purpose, aside from taking control of the administration, had been to create a crisis that was calculated to restore unity. It is most unlikely that he either expected or wanted war with Europe—a foreign crisis only, not war, would have served his purpose. It was a dangerous strategy, however, and it is just as well that Lincoln rejected it. Although the memo remained confidential, Seward's foreign war panacea was well known among diplomats and merely confirmed their view that Seward would be a difficult person with whom to deal.
Seward's memo stemmed partly from his disagreement with his fellow cabinet members over the question of maintaining federal control of Fort Sumter in the harbor of Charleston, South Carolina. The fort, well within the range of shore batteries, could not be defended, and when President James Buchanan had attempted to send provisions to the fort early in January, Confederate gunners opened fire on the supply ship Star of the West, forcing it to retreat. Buchanan left the question of reprovisioning the fort or evacuating it to his successor, and shortly after Seward took office, he recommended the evacuation of Fort Sumter. Initially, Seward had majority support in the cabinet. He argued that attempting to resupply the fort would be regarded as a hostile act against the Confederate States of America and would not only strengthen the separatists' hands but also cause critical border states, such as Virginia, to secede from the Union. Lincoln, however, did not agree. He had pledged that he would yield no federal property to the Confederate government and decided to let events help him decide on a course of action. Over the following few weeks, public sentiment for holding the fort strengthened, and by the end of March, a majority of the cabinet came to the same position. This isolated Seward, who still counseled delaying any confrontation and who now feared that attempting to reprovision the fort would lead to war. His memo was his last effort to dissuade Lincoln from sending fresh supplies to the fort.
On 6 April, Lincoln notified South Carolina authorities that he had dispatched a supply force to Fort Sumter. Four days later, South Carolina demanded that the commandant of the fort, Major Robert J. Anderson, immediately surrender. When Anderson offered to surrender only after a few days when his supplies ran out, the Confederates, aware that fresh supplies were in transit, rejected Anderson's offer. On 12 April, Confederate General Pierre G. T. Beauregard opened fire on Fort Sumter. As Seward had feared, the decision to hold on to the fort had provoked the Confederates. The Civil War had begun.
Following the outbreak of hostilities and Jefferson Davis's announcement on 17 April that the Confederacy would issue letters of marque and reprisal, creating privateers for action against Union shipping, Union policy changed. Lincoln responded to Davis on 19 April by announcing that the Union would treat privateers as pirates and proclaiming a blockade of Southern ports. Seward attempted to open negotiations with the British foreign minister, Lord John Russell, for American adherence to the Declaration of Paris of 1856, an international agreement that, among other things, outlawed privateering. The United States had declined to participate earlier because, as a small-navy nation, it wanted to hold on to the privateering option. Seward hoped that the negotiation would cause Britain to postpone recognition of the Confederate belligerency and that an Anglo-American convention committing the United States to the Declaration of Paris would require Britain and other nations to treat Confederate privateers as pirates. Negotiations, however, began on 18 May, four days after Britain had recognized Confederate belligerency and collapsed in July, when Russell announced that if negotiations with the Union were successful, Britain would neither hold the Confederacy to the agreement nor treat Confederate privateers as pirates.
Lincoln's blockade proclamation had an important effect on British policy. A blockade was universally regarded as an act of war and therefore an implicit recognition that a state of belligerency existed. Therefore, Lincoln's proclamation opened the door to a British proclamation of neutrality and recognition of Confederate belligerency, which (except when in violation of neutrality laws) gave the Confederate States the right to, among other things, solicit loans, buy arms, engage in recruiting, and put cruisers on the high seas with the rights of search and seizure. Because British commerce with the United States and reliance on Southern cotton was so heavy, Russell had to respond to Lincoln's proclamation. The British proclamation became public on 14 May 1861, and as Seward had feared, the other nations of Europe immediately followed with their own proclamations of neutrality. The way was now clear for Confederate agents to scour Europe for money and material to conduct their war.
The Union blockade was a double-edged sword. If effective, or even moderately effective, it would reduce the ability of the Confederates to import war material. But it would also interfere with foreign commerce and deprive Britain, France, and other industrialized nations of vital supplies of cotton. Reducing the export of cotton to Europe could increase pressure in Europe for involvement in American affairs in support of the Confederacy, which the Confederates hoped and expected would be the case.