How might Britain obtain a US apology over U-2 spy flights and persuade the Soviet leadership to back away from threatening Pakistan?
Short answerFind something each power wants more, then make access to that objective conditional on the apology or restraint Britain seeks.
NotesDiplomacy here is a search for competing priorities rather than a demand for goodwill. To obtain a US apology over U-2 spy flights, Britain would need something Washington wanted enough to accept the political cost of apologizing. To discourage Soviet threats against Pakistan, it would likewise need to connect a more important Soviet objective to restraint. The exchange makes leverage conditional: the desired concession becomes the price of access to the more valuable goal.