Constantine thought about it a lot, but standing in his position, his thinking would be different from an average person. His effort and calculations were infallible, but there were too many unknown variables.
The five destined ones were one problem. If he had known earlier, he would have first killed the five of them, but he had been too conceited. Standing at such a height, and holding this much power, he would have definitely ignored these youths. But in actual fact, the five of them had managed to shake the whole Milky Way Alliance.
Second point: Atlantis had not moved. This surprised Constantine. All along, the two countries had good relations. However, Atlantis was decisive when it was time to choose. This was a huge blow to Aslan, but it was not too surprising. He had plans prepared for this, but it did have an effect.