There is indeed a decline of faith in the modern world. If not a decline of faith, perhaps the problem arises in the increase of erroneous faith to other gods and/or personal beliefs. In the past, people fought in defence of religion. Those men/women were known as martyrs, and later canonized as saints. Then there was a shift from religion to the defence of the country. Men who showed such love of country were proclaimed national heroes. Supposedly, the product of the two - martyrs and heroes - would resemble a sort of superman, an ideal being; one who is driven by his faith with deep concern for the welfare of the world. However, it seems that modern men had twisted this concept; consequently mutating it into one of the world's greatest villain - terrorism. To untwist such a knot, St. Thomas Aquinas would put emphasis on the principal end of man that was still supernatural, the importance of the salvation of man's soul. Aquinas would fight the war on terrorism with spiritual weapons - a crucifix in one hand and a bible in the other. .
St. Thomas Aquinas lived in the time of martyrs. Don't get me wrong, although times have changed, the saying "history repeats itself" is undeniable. Despite this fact, Aquinas remained pure amidst the corruption with which he was surrounded, and he resolved to embrace the religious life. In addition, today Aquinas would preach the Word of God to the world, with emphasis to the people of the United States, Iraq and the surrounding countries greatly affected by the on-going war on terrorism. His sermons were known to be forceful, redolent of piety, full of solid instruction, abounding in apt citations from the Scriptures. This is the kind of zeal our world needs to fight against terrorism. .
The way I have come to understand Aquinas is that he wouldn't say anything directly to the leaders involved. He would probably preach through example. His tactic would most likely be to hit them indirectly through a coalition of prayers around the world.