The emmigrants from the late 1800s and early 1900s were from many European countries and English was the only "common" language, so they all eventually learned English. Also, the difference today is the overwhelming numbers of Hispanics. There wasn't the overwhelming numbers from just one European country. They also WANTED to assimilate into America, not change America to be like their "Old Country". Lot of difference today, just the shear numbers, and they are not as well educated as the Europeans were.
Also, another thing. English is spoken as a first or second language by 800,000,000 people in the world. It is spoken not only here, but most of the former British colonies. It is also the "official" language of India since India was a former British colony. India also had 7 major languages so they use English as their standard. Only Mandrian Chinese is spoken more, but it is all concentrated in one country. In most European countries English is required to graduate high school. English is the international business language, the international airline language, the international scientific language, and the international internet language. Spanish is the 3rd most widely used language because of the old Spanish colonies in Central and South America, and in the Philipines. However, most Hispanic countries are more poor and under educated in comparison to European nations, even 100 years ago.