If you are asking what 9/11 was about, it was the day when the twin towers got hit by 2 planes, and was stated as a terroist attack.
Here is the answer to the given question above. The technological advance that allowed cities to expand outward are the <span>forms of electric urban transportation. Electric urban transportation includes the mode of transportation that we are seeing today. Hope this answers the question. Have a great day!</span>
Not:
Invasion of Poland
Nazi-Soviet Non-Agression Pact
Pearl Harbor
Munich Conference
The rest are all associated with WW1
hope this helps