What is Keynesian economics, pt 2

From Wikipedia

Precursors
Keynes's work was part of a long-running debate within economics over the existence and nature of general gluts. While a number of the policies Keynes advocated (notably government deficit spending) and the theoretical ideas he proposed (effective demand, the multiplier, the paradox of thrift) were advanced by various authors in the 19th and early 20th century, Keynes's unique contribution was to provide a general theory of these, which proved acceptable to the political and economic establishments.

Schools
An intellectual precursor of Keynesian economics was underconsumption theory in classical economics, dating from such 19th century economists as Thomas Malthus, the Birmingham School of Thomas Attwood, and the American economists William Trufant Foster and Waddill Catchings, who were influential in the 1920s and 1930s. Underconsumptionists were, like Keynes after them, concerned with failure of aggregate demand to attain potential output, calling this "underconsumption" (focusing on the demand side), rather than "overproduction" (which would focus on the supply side), and advocating economic interventionism. Keynes specifically discussed underconsumption (which he wrote "under-consumption") in the General Theory, in Chapter 22, Section IV and Chapter 23, Section VII.

Numerous concepts were developed earlier and independently of Keynes by the Stockholm school during the 1930s; these accomplishments were described in a 1937 article, published in response to the 1936 General Theory, sharing the Swedish discoveries.

Concepts
The multiplier dates to work in the 1890s by the Australian economist Alfred De Lissa, the Danish economist Julius Wulff, and the German American economist Nicholas Johannsen, the latter being cited in a footnote of Keynes. Nicholas Johannsen also proposed a theory of effective demand in the 1890s.

The paradox of thrift was stated in 1892 by John M. Robertson in his The Fallacy of Savings, in earlier forms by mercantilist economists since the 16th century, and similar sentiments date to antiquity:

Today these ideas, regardless of provenance, are referred to in academia under the rubric of "Keynesian economics", due to Keynes's role in consolidating, elaborating, and popularizing them.