The correct answers are: 3. The Mexican-American War and 2. Discovery of gold at Sutter’s Mill.
Indeed, American settlers had kept going further west; they settled the Mexican state of Texas and became the majority. They ended up seceding from Texas and were an independent republic for 8 years, after which they entered the Union. This provoked a declaration of war from Mexico. The war was won by the United States and in 1848 the Treaty of Guadalupe Hidalgo made official the Mexican Cession which gave all the American Southwest to the Union. This made the US a transcontinental nation and settlers started pouring in.
One of these settlers, James Winston Marshall, discovered gold in the Flakes Mountains, in a property owned by John Sutter. The news of the gold became global and hundreds of thousands of new settlers came in search for fortune.
