Finally, two events occurred in rapid succession that destroyed the alliance completely: first, in July 1800, the British seized a Danish frigate, prompting Paul to close the British trading factories in St. Petersburg as well as impound British ships and cargo; second, even though the allies resolved this crisis, Paul could not forgive the British for Admiral Nelson's refusal to return Malta to the Order of St. John, and therefore to Paul, when the British captured it from the French in September 1800. In a drastic response, Paul seized all British vessels in Russian ports, sent their crews to detention camps and took British traders hostage until he received satisfaction. Over the next winter, he went further, using his new Armed Neutrality coalition with Sweden, Denmark and Prussia to prepare the Baltic against possible British attack, prevent the British from searching neutral merchant vessels, and freeze all British trade in Northern Europe. As France had already closed all of Western and Southern Europe to British trade, Britain, which relied heavily upon imports (especially for timber, naval products, and grain) felt seriously threatened by Paul's move and reacted fast. In March 1801, Britain sent a fleet to Denmark, bombarding Copenhagen and forcing the Danes to surrender in the beginning of April. Nelson then sailed towards St. Petersburg, reaching Reval (14 May 1801), but after the conspiracy assassinated Paul (23 March 1801), the new Tsar Alexander opened peace-negotiations shortly after taking the throne.