Write the possessive noun for:

the habitat of the kangaroos

is kangaroo's habitat or
the kangaroos' habitat

The idea of this excerpt from John F. Kennedy’s speech is encouragement—encouragement to fight for what is right, and what is right is freedom for all of humanity.  This idea is introduced to us by the words “defending freedom,” which appear at the beginning of the excerpt.   The idea is also reinforced at the end of the excerpt with the imperative statement that implores citizens of the world to ask “what together we can do for the freedom of man.”