Immigration into America started in the 1600s and continued nonstop and unrestricted until the late 1800s. Since the United States was a new nation with a massive frontier and very few people to shape it, immigration was encouraged. By 1882, however, the expansive frontiers and open spaces were quickly disappearing. A country that had once had room for all was full, or so its citizens thought. Passing restrictive immigration laws was their way of closing the "Golden Door" on the constant stream of immigrants. With the passage of time, these laws became increasingly more strict, and by 1921 the first US immigration quota system had been introduced. In essence, the quota system allowed only a pre-set number of immigrants to enter the country yearly. As time passed, stricter and stricter regulations were imposed, until the annual quota reached an all-time low in 1960—of about 500,000. Illegal aliens have been a problem ever since the first immigration restriction was imposed, but the problem has never been as serious as it is now. No one really knows just how many illegal aliens are living in the United States. Estimates of the illegal population range from a low of about two million to a high of ten million, and this population is growing. Estimates of the number of "illegals" entering each year vary from 100,000 to 500,000. The problem has grown to such proportions that there are nearly as many immigrants entering the United States today as there were at the turn of the century. According to one Immigration and Naturalization Service (INS) authority, in fact, "America has lost control of its borders."