I think for 20th century, Connected is a good example of people extending their boundaries and finding it easier to interact. The 20th century bought about many fantastic ideas for technology...
We are connected at every place
I'm already with you, too, thinking about these words
How many treasured words can we have with each other
By the time we sleep our eternal sleep?
For 21st century either Mirrorcle World or Startin'. MW is kinda obvious but for Startin', I think it's an accurate description of people in the modern world being able to believe they can achieve anything.
There is no point in comparing yourself with someone else
Because everyone has one's own measure
You are the only one in this world
No one can replace you
If you still hesitate
It's really up to you
Sparkle is also a good choice!
I get so torn over Ayu's lyrics >_<;;