About NCMA. NCMA is the national trade association representing the producers and suppliers of concrete masonry products, including concrete block, manufactured stone veneer, segmental retaining walls and articulating concrete block. For over 100 years, the Associationâs mission remains to advance, protect and promote the common interests of its members.
Between 1803 and 1853, the United States almost tripled in size. In the early 1800s, the land west of the United States was very undeveloped.
Some historians differentiate between a first Great Migration (1916â1930), which saw about 1.6 million people move from mostly rural areas to northern industrial cities, and a Second Great Migration (1940â1970), which began after the Great Depression and brought at least 5 million peopleâincluding many townspeople with urban skillsâto the north and to California and other western states.