Napoleon seemed unstoppable until two separate campaigns failed. He gathered a huge army to invade and conquer Russia in 1812. His army was caught by the Russian winter and destroyed by the weather and lack of food. The countries of Eastern Europe, led by Austria and Prussia, began to ally against him, forcing his troops back towards France. Meanwhile, a small army in Portugal and Spain, led by Arthur Wellesley (later to become Duke of Wellington) began to push Napoleon’s troops out of Spain.