The challenge is to push the development of world's cities upward, not outward.
So
That by the year 2000, arcologies 500 meters high that house tens of thousands of people are considered normal.
This should happen not just in first world countries, but also second or third, like Mexico, Brazil, Egypt, India, Indonesia, and China.
POD preferably post-WW2, but shortly before it can be accepted.
Thanks in advance!