Help with Understanding Sir Isaiah Berlin

If anyone has read "Churchill and Roosevelt" by Sir Isaiah Berlin (from Winston Churchill in 1940) could you please explain:

1. According to Berlin, who are the great imaginary minds of each of the two great wars, WWI and WWII? What's the difference between the two groups?

2. What according to Berlin, are the differences between Roosevelt and Churchill? How do both show imagination?

3. How do their imaginations fuse "isolated beliefs"

4. In what ways does Roosevelt represent an "American" attitude? Can you discern any reason for the difference in American and British attitudes?

~~Thanks so much

Edit [Moderator]: Moved from "General" to "History"