Which technological advancement most strongly affected a leader's speech during world war ii?

I believe the answer is: The Radio

Prior to the development of radio, the leader's speech is limited for the people who are physically present in the building or the field where the speech is given.

After the development of radio, the leader's speech could be heard from various places all over the nation.

if its apex this should be the correct answer

war information to be released publicly must first be deemed useless to the enemy

so are you asking to write a page on why its so wrong?