You can EMP blast whole continents with it. It is thought that in case of an all our nuclear attack at high up detonation like that would happen early one to disable as many electronics and communication facilities of the enemy.
Then of course countries have been working on EMP hardening military tech.
For example https://en.wikipedia.org/wiki/Nuclear_electromagnetic_pulse says that:
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if the Starfish Prime warhead had been detonated over the northern continental United States, the magnitude of the EMP would have been much larger (22 to 30 kV/m) because of the greater strength of the Earth's magnetic field over the United States,
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Then the Soviets also "played" around with that too:
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The monitored telephone line was divided into sub-lines of 40 to 80 kilometres (25 to 50 mi) in length, separated by repeaters. Each sub-line was protected by fuses and by gas-filled overvoltage protectors. The EMP from the 22 October (K-3) nuclear test (also known as Test 184) blew all of the fuses and fired all of the overvoltage protectors in all of the sub-lines.[15]
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