That’s an insanely complex question since volumes have been written about the Church’s involvement in modern politics. I’ll recommend a few things for you to read.
Pope Leo XIII’s encyclicals encompass a wide variety of political topics, ranging from the effect of Atheism, Nihilism, and Socialism on society, to the necessity of preserving the institution of Marriage, to the proper ordering of a Christian society, and the dignity of labor and how to preserve a proper relationship between capital and labor. Check out this website for his work:
papalencyclicals.net/Leo13/index.htm
The Popes following him wrote extensively about similar matters; check out the encyclicals that followed in the wake of Leo XIII’s inauguration of modern Catholic social thought: Quadragesimo Anno (Pius XI, 1931); Mater et Magistra (John XXIII, 1961); Pacem in Terris (John XXIII, 1963–his last work); Populorum Progressio (Paul VI, 1967); Sollicitudo Rei Socialis (John Paul II, 1987); Centesimus Annus (John Paul II, 1991–written to commemorate the 100th anniversary of Pope Leo XIII’s Rerum Novarum, it describes how what is put forth in Rerum ultimately led to the downfall of Communism); Deus Caritas Est (2005, Benedict XVI); Caritas in Veritate (2009, Benedict XVI).
These may all be found at the above website.
Finally, the decrees of the Second Vatican Council had much to say about this area. Check out Gaudium et Spes, the Pastoral Constitution on the Church in the Modern World, as well as Dignitatis Humanae, the Declaration on Religious Freedom.
In addition to this, there are hundreds of Catholic political philosophers worth reading. St. Thomas Aquinas had a broad body of political work, and it is his formulation of the just war doctrine that we still employ today. St. Augustine wrote City of God, which is one of the earliest Catholic political documents. While older, these works help to inform our modern philosophy.
Finally, for someone whose philosophy hits home for Americans, read Archbishop Charles Chaput’s Render Unto Caesar, about Catholic participation in American political life.
Hope this helps!
-ACEGC
