In 1517, Martin Luther nailed his 95 Theses to the door of the Wittenburg castle church and began the Protestant Reformation and over the next 15 years, many Germans inside the Holy Roman Empire converted to Lutheranism. In 1531, several of the small principalities and electorates forged a defensive alliance, the Schmalkaldic League (named for the town in Thuringia where the pact was signed) against the inevitable backlash by the Catholic Holy Roman Emperor Charles V.
In the early to mid sixteenth century, Charles V was the most powerful man in Europe. In addition to being the Holy Roman Emperor which conferred significant authority over most of Central Europe, he was the sole inheritor of three of the largest dynasties of Europe: Hapsburg Austria, Valois-Burgundian Netherlands, and Trastamara Spain, including most of Italy, the Balkans, and the New World. To keep these possessions, he was constantly at war with his archenemies Francis I of France and the Ottoman Sultan Suleiman the Magnificent, among many others in this age of rapidly shifting alliances.
However, as long as the Schmalkaldic League confined its activities to matters of religion, e.g. converting the population, confiscating Church property, murdering priests, nuns, and monks etc., Charles had little issue with Protestantism. He had fought more than one war against the Pope. However, by the mid-1540s, the defeated and humiliated Francis I was actively supporting the Schmalkaldic League even as he was slaughtering Protestants in France. Eventually, the League turned political with the goal of creating a Protestant entity to supplant the Holy Roman Empire. This Charles could not tolerate. In 1547, Charles V invaded Saxony to capture the ecclesiastical center of Lutheranism, Wittenburg, and defeat the League’s army under the Elector of Saxony John Frederick I, and Landgrave Philip I of Hesse. The rest of the free cities and smaller states of the League would then fall into line.
The League’s army was small, unprofessional, inexperienced, and lacked any unity of command as each contributing state, no matter how small, had an equal say in command. Charles’ army was the exact opposite. His army was composed of veterans almost to a man. They had fought nonstop for twenty years. They halted the Ottomans at the Gates of Vienna, threw the French out of Italy, and nearly captured Paris. Furthermore, his was a multicultural army that reflected his dominion: He had German landsknechts and Catholics, Protestant soldiers from loyal Imperial electorates, Italian condottieri, and Dutch musketeers and armsmen, all centered around and organized by the steely and tough Duke of Alba, the commander of the premier shock troops in the early Age of Pike and Shot: the Spanish tercios.
The tercio was the first formation in Europe specifically designed to combine the firepower of gunpowder in the form of arquebuses, the defensive power of the pike or polearm, and the counteroffensive power of a heavily armed swordsman to defeat a charge of armoured knights, like the French gendarmes. Named a “tercio” because theoretically it was composed of 1/3 of each, the formation mixed companies of each of the three arms into combined columns, or in Italian, “colonna”, led by a “coronel”, which is Spanish for a senior (and noble) commander of a column of companies. (The combination of the two words gives us the modern word “colonel” and its unique pronunciation.) The Spanish tercios were the most feared, dangerous, and professional heavy infantry on the planet in the 16th and early 17th centuries, and they were led by arguably the best commander of the age, Fernando Alvarez de Toledo, the Duke of Alba. The army of the Schmalkaldic League didn’t stand a chance.
On 24 April, 1547, the ailing Charles V (who was carried into battle on a litter, not majestically on a horse as in Titian’s famous portrait) and his Imperial army led by the Duke of Alba reached the Elbe River opposite Muehlberg. Elector John Frederick with the Schmalkaldic Army outside the town, thought he had time to organize. But his pickets on the far bank were forced to retire by the longer range of the Spanish and Dutch arquebuses and his men lost visual contact with Imperial Army, though this wasn’t reported to him.
While he went about attempting to assemble his bickering army, the Duke Alba was well on his way to crossing the river without using the obvious stone bridge. Some enterprising Spanish veterans swam the river and collected boats, which they used to build another bridge. Additionally, Maurice of Saxony, a Protestant who hopped to gain from John Frederick’s loss, convinced a discontented peasant to identify a ford. Maurice then took all of the cavalry across the river, with each rider carrying an additional arquebusier. By the time John Frederick knew what was happening, he had light cavalry behind him, was under fire from the woods to his flank, with the tercios approaching from the front, and missed the only opportunity to even conceivably win the battle by attacking the vulnerable river crossing. The Schmalkaldic Army broke after a quick fight and the cavalry ran down the defenders, killed thousands, and captured the leadership.
John Frederick and Philip lost their electorates, and the rulers of the other states were replaced. Wittenerg was captured and the majority of the influential Protestant thinkers fled to other parts of Europe, where they would continue to proselytize. The Battle of Muehlberg and the end of the Schmalkaldic War shattered Protestantism, but inadvertently caused it spread, most notably to England, where German refugees became influential members of the English Reformation under King Henry V. Protestantism would not only spread but fragment as a result.
The sick and exhausted Charles eventually settled for the Peace of Augsburg in 1555 with the Protestants, which allowed each electorate to choose its own religion as long as they accepted the Holy Roman Emperor’s authority. After the Peace of Augsburg, Charles V ruled over the largest (mostly) willing multicultural European empire not seen until 458 years later with the signing of the Lisbon Treaty in 2009 which established the European Union as a legal entity. He would die shortly afterwards and wouldn’t live to see it fall apart.