When Kaja Kallas became Estonia¡¯s prime minister she thought foreign policy was her weak spot. So she got to work. With recommendations from other leaders, Kallas drew up a study program. And she¡¯s still at it.

She¡¯s currently reading a history of Iran and has plowed through works by Margaret Thatcher, Henry Kissinger and a biography of Ukraine¡¯s Volodymr Zelenskyy this year ¡ª as well as books about the Middle East, Israel-Palestine and Taiwan. Graham Allison¡¯s "Destined for War," on the dangers of the U.S.-China rivalry, was suggested by the NATO secretary-general.

Foreign policy, she told Adam Grant on his Re: Thinking podcast last year, "is not my weakness anymore.¡±