We find from Scripture that there is a connection between angels and the different nations of the world. When the Jews were about to return from captivity, the prophet Daniel began to pray and fast for their return. At this time the Jews were under the rule of the Persian empire. After three weeks of prayer, an angel appeared and explained to Daniel the reason for the delay.  

But then a hand touched me and roused me to my hands and knees. He said to me, "Daniel, greatly beloved, pay attention to the words that I am going to speak to you. Stand on your feet, for I have now been sent to you." So while he was speaking this word to me, I stood up trembling. He said to me,  "Do not fear, Daniel, for from the first day that you set your mind to gain understanding and to humble yourself before your God, your words have been heard, and I have come because of your words. But the prince of the kingdom of Persia opposed me twenty-one days. So Michael, one of the chief princes, came to help me, and I left him there with the prince of the kingdom of Persia, and have come to help you understand what is to happen to your people at the end of days. For there is a further vision for those days." But I am to tell you what is inscribed in the book of truth. There is no one with me who contends against these princes except Michael, your prince (Daniel 10:10-14,21).

Spiritual Battle

This passage gives us some insight into the battles occurring in the spiritual realm. It took this angel twenty-one days to answer Daniel's prayer because he was hindered by the prince of the kingdom of Persia. Obviously this could not have been an earthly prince restraining an angel.

Overseeing The Nation

The prince of Persia seems to be the angel that was overseeing this nation. For some reason he was opposed to the Jews returning to their Promised Land. Though no specific details are given, we are informed by this passage that there was an angel overseeing Persia in the same way as Michael was the overseer of the nation Israel.

Prince Of Greece

From this passage we are informed that there is also a prince, or angel, over Greece.

Then he said,  "Do you know why I have come to you? Now I must return to fight against the prince of Persia, and when I am through with him, the prince of Greece will come (Daniel 10:20).

After his battle with the prince of Persia, this angel said the angel, or prince, of Greece was to come. This angel that looked after Greece, like the one over Persia, was not inclined to let the Jews be released from their captivity.

Rulers

When the New Testament uses the word "rulers" to describe the orders of angels, this may include these various angels over the nations. The word is used of both good and bad angels. Paul wrote:

so that through the church the manifold wisdom of God might now be made known to the rulers and authorities in the heavenly places (Ephesians 3:10).

He said that our ultimate struggle is against these authorities.

For our struggle is not against enemies of flesh and blood, but against the rulers, against the authorities, against the cosmic powers of this present darkness, against the evil spiritual forces in the heavenly places (Ephesians 6:12).

Summary

Scripture indicates that Michael the archangel looks after the nation Israel. There are also other angels that oversee the various nations. Scripture gives examples of angels looking over the affairs of Greece and Persia. These orders of angels are perhaps the rulers that Paul referred to when he said that our struggle is with spiritual forces.