The correct answer is the fourth one: They resulted in higher casualty rates than in the past.
The WWIleft between 9 and 10 million dead and 20 million hurt soldiers. Additionally, it is estimated that civilian victims rise to 7 million. It was the first time in history that a war left such a massive number of victims and it was due to the use of new military technology. At first, the war was a clash between 19th-century technology against 20th-century technology, but in 1917 all the great armies, that added millions of men in their ranks, were modernized. The war became a competition for the creation of the most lethal weapons. To the German invention of submarines, advanced artillery, and poison gas, which killed thousands of soldiers and civilians as well, the British created the first aircraft carrier and the first tanks. For these reasons, the WWI was the most lethal war in History before the WWII.
A cause was that Texas declared its independence from Mexico. It changed the U.S. by the U.S. gaining California, New Mexico, Utah, Arizona, Colorado and parts of Wyoming.
The majority of immigrants who arrived in the United States between 1800 and 1860 came from "<span>(3) northern and western Europe" although this shifted slightly later. </span>