The king’s heart is in the hand of the Lord; like rivers of water he turns it wherever he wishes. Proverbs 21:1
There are many instances in history in which the leader of a nation has changed his mind or acted against his own best interests in a way that leads people to believe God must have been at work.
Such an example could be the decision by Hitler not to launch an invasion of Britain (which might have won him the war), but rather to turn on his ally Stalin.
An even better example might be the about face of Stalin after World War II. Previously his government had been anti-zionist, but now he began to sponsor the cause of a Jewish homeland; the Soviet Union voted for the Palestine partition plan in the United Nations, under the illusion Israel would become a socialist state.
Truman, harking back to his Christian upbringing, quickly recognized the fledgling Israeli nation, although the State Department urged against it.
It was time for Israel to be reborn, and God moved the hearts of rulers to bring it about.
Until the end of his life, Christ had little contact with kings, rulers and governors. Nonetheless, that Pilate yield to the roar of the Jerusalem mob was necessary for our salvation, and turned his heart to do what he knew was wrong.
Following his resurrection God also turned the heart of kings. The first ruler recorded as accepting Christ was not a king, but the the proconsul Sergius Paulus on the island of Cyprus. Within three centuries, the history of Europe and Asia Minor would become a history of kings who bowed their knees to the Lord and brought their nations into the fold of Christendom, beginning with Armenia in the third century and ending with Lithuania in the fourteenth.
We cannot presume to determine why God has not chosen to turn the hearts of other kings to Christ. But as the history of this age draws to a close and we see prophecies fulfilled, we likely will get deeper insight into God’s plan.