reasons for detente (day-taunt)

europe

russia

usa

security of borders due to international affirmation of post-war european borders

national security due to post-war affirmation of european borders

economic challenges brought by the expenses of nuclear weapons

a reason to end the Vietnam War due to the mass casualties and economic challenges, as well as internal opposition

economic challenges brought by the expenses of nuclear weapons

China

China wanted better relations with the US to gain leverage over the USSR

Western technology + resources

To regain Taiwan

rebuild relationship with China after Sino-Soviet split as a partnering communist country

build relationship with China to bring them into the international diplomatic landscape as leverage

demonstrate civil foreign policy

ensure eastern countries follow their human rights standards

worried about their own safety due to the nuclear war

minimise further damage after post-war casualties, furthered by their citizens' recent memories of a terrible war

willy brandt was a key supporter of better soviet relations with the west and for a better developed relationship between East and West Germany