Through the 800s, 900s, and part of the 1000s, the papacy grew in power and corruption. This period was also one of great instability in the Catholic Church as decisions were often made for political reasons as many popes were essentially appointed by the Holy Roman Emperor. Also during this time missionary work became a very important role of the church as numerous kings converted to Christianity, including kings in Hungary, Poland, and Denmark, truly expanding the influence of the Catholic Church, but also the power and wealth of the Holy Roman Emperors. Despite the growth in power for both, they often argued over numerous issues as the relationship between these two entities seems debatable as it shifted from positive to negative. This essentially ended in 1177 when the Papal States were officially recognized by the Holy Roman Empire.
The Catholic Church also had detractors in the east during this time as the Christian Orthodox church separated from the Catholic Church in 1054, an event known as the Great Schism. Also during this time the Crusades began, a series of wars to take over the "Holy Land," beginning in 1095. Most of the Crusades were led by kings from throughout Europe, not by the popes or the church, although they often approved of the crusades and took a secondary role in many of them.
The instability continued into the 1200s and 1300s as political rule forced the pope to flee to numerous cities, as the pope was rarely positioned in Rome. Among the most famous of these foreign locations was Avignon, France, which is where Pope Clement V moved the papacy in 1309. The papacy moved back to Rome in 1378, but many of the French argued this move and two popes were elected one Italian and one French, often referred to as the "Western Schism." This ended in 1417, when the papacy was permanently moved to Rome (although Pope Benedict XIII of France continued to make unrecognized papal decrees until his death in 1423).
The power of the Catholic Church and the popes continued to grow into the 1500s as Europe stabalized. During the time the church also gained more influence throughout Europe, but didn't directly control much of the territory of the Papal States. In fact, many of the Papal States were ruled over by local princes, many of whom fought with each other regularly.
During this same time the church grew incredibly corrupt as many popes appointed their nephews to the position of Cardinal, giving them opportunities to become the next pope. This created a system, in which the popes and cardinals were quite wealthy and powerful. They began selling indulgences (receiving money for admission into heaven) and became closely connected to wealthy Italian families. While this process hurt the reputation of the church, eventually leading to the Protestant Reformation, it also vastly increased its wealth, influence, and power of the church.
With greater wealth, the popes solidified the Papal States as they built armies, commissioned numerous Renassiance artists, and continued to expand their influence. Through taxation of the Papal States, the wealth of the church grew to incredible numbers and Vatican City built to a vast degree in the Rennaissance style. However, with this came vast amounts of corruption as some popes bribed their way to the papacy and others fathered children. This ended in 1527 with the sacking of Rome by the Holy Roman Emperor and the beginning of the Protestant Reformation in 1517.
The fall of Rome and the Reformation were the direct result of corruption in the church as well as unorganization in the Papal States and papacy. The pope could no longer maintain power over the many prince-ruled Papal States as he had no army and the people throughout Europe grew tired of the selling of indulgences, corruption, excessive money spent, and the loss of morality in the church. This led to Martin Luther's "95 Theses" and the beginning of the Protestant churches.
In the late 1700s changes again continued in Europe as revolutions swept through numerous countries, including France. The French took papal possessions in Avignon and invaded Italy with an agenda quite lliberal compared to the tenants of the Catholic Church. These attacks led to the fall of the Papal States, but after the Napoleonic Wars ended in 1814 the Papal States were returned, but not without massive social changes and desired changes by the people.
Throughout the 1800s the popes and Catholic Church walked a thin line, balancing desired social changes with political changes in Italy and Europe as a whole. Over time tension between the church and the Italian people grew as anti-Catholic tendencies were magnified. This led to a growth in power of the many small Italian states as they united Italy in 1861 and a loss in power by the Papal States and Catholic Church. This tension peaked in 1870 when the unified Italian state defeated the Papal States and moved their capital from Florence to Rome. Sharing a city with the conflicting Roman government and losing their possessions, the papacy found itself in a corner.
After the unified Italian state took Rome the pope refused to become an Italian citizen so essentially became a prisoner in the Vatican, as this "Roman Question" remained unresolved into the 1900s. During this time the popes refused to submit to Italy and essentially remained imprisoned in the Vatican.
Although the papacy and church seemed cornered in Italy itself, it found many allies in other European countries who were either at odds with Italy or, more commonly, sought a conservative force in the liberal movements of Europe at the time. In this way the Catholic Church acted as the counter-balance to the liberal movements of Europe and found their greatest supporter in France, but also from other monarchs. However, the church also wisely supported many worker's rights and the lower classes, gaining greater support and power elsewhere in Europe, without overstepping their bounds and causing instability in any country with a monarch that supported the pope and the Catholic Church.
Despite the conflicts between the Catholic Church and Italy, no violence was undertaken and the two sides seemed resolute in their stances; the popes refused to recognize Italian soveigrenty and Italy refused to give the popes any power and took many of their possessions in Rome and throughout Italy. This conflict, often known as the "Roman Question" finally came to an end in 1929 with the Lateran Treaty. In this treaty the Holy See gave up all claims on the former Papal States and declared neutrality while Italy recognized Vatican City as an independent country and established Catholicism the religion of Italy.
Despite the treaty, the two side continued to argue, especially due to Benito Mussolini's facist government. Despite actually signing the Lateran Treaty, Mussolini's political stances put him in direct contridiction to the Holy See and Vatican City. This continued into the 1930s as Italy and Germany allied and the Holy See regularly spoke out against Nazi acts.
With the outbreak of World War II in 1939 Vatican City remained neutral and both sides recognized this. The Facist Italian state allowed Vatican City's neutrality, then the Nazis occupied Rome and left the Vatican alone, then the Allies occupied Rome and again left Vatican City alone.
After World War II Pope Pius XII changed directions for the church as he welcomed cardinals from all continents and made the Holy See much more inclusive of all Catholics, no matter their ethnicity or nationality. He also faced difficulties as numerous communist governments outlawed religions and prevented the worship of Catholicism. Many Catholic priests were also killed during these years, particularly in the Soviet Union and China. In this way, the Holy See became almost anti-communist, although on paper they maintained their neutrality and remained focused on the Catholic faith and its adherants.
In 1962, under Pope John XXIII, the Second Vatican Council took place, undertaking a huge number of reforms in the Catholic Church. For most Catholics today the most noticeable change from this council is the fact that masses are now done in the local language instead of in Latin. Of course this was just one of many changes brought forth from this council. Changes continued in 1965 when the Catholic and Orthodox churches finally recognized each other.
The conflicts with communism became more pronounced when in 1978 the College of Cardinals elected Pope John Paul II as pope, a Polish citizen and the first non-Italian pope since the 1500s. Coming from a communist country, the pope made great strides in working with governments from the east and west to cooperate and communicate. Pope John Paul II also revitalized the church in many ways as he traveled extensively and encouraged the Catholic youth of the world to become more active members of the church and their local communities.
After the death of Pope John Paul II in 2005, Pope Benedict XVI from Germany was elected pope, but stepped down in 2013, leading to the election of Pope Francis, from Argentina.