Vacuum Valley in California. Thermionic valves are highly sensitive to vibration when working, in addition to having a limited lifetime. The working lifetime can be extended by having multiple heaters in a valve. Helium is a major strategic resource, being evolved from radioactive ores - USA, USSR, Australia, South Africa.
Intercontinental travel is slower, though rockets can still transport weapons of mass destruction.
To compensate for this the rail network in USA is far stronger. This makes oil less of a strategic resource, though it is still widely used in plastics. There is a cold war between USA and USSR, with Europe divided. The corporations maintain economic links around the world despite political frigidity. WWII ended in 1944, shortly after the excommunication of Hitler lead to Italy abandoning the war and Germany splitting along religious lines.