1)
What is astonishing?
1.
Malbim: (a) Bavel scattered all nations to shards. How did they gather again for war?! Where is the hammer that shattered their connection?! (b) How is Bavel desolate among the nations? It always had great, mighty nations to help it!
2)
Why is Bavel called "Patish Kol ha'Aretz"?
1.
Rashi: It used to shatter everything. Radak - and now, it is shattered!
