Most of the Amiga and Atari ST games that were actually developed for those systems came from Europe. There were exceptions in the mid-to-late 80s. Dungeon Master was an ST original, the Cinemaware classics like Defender of the Crown and The Three Stooges were all Amiga originals. I believe MicroProse and some of Electronic Arts' developers had a few Amiga originals, but virtually all the US developers/publishers transitioned from the 8-bit machines to the PC, Amiga, ST, Macintosh and the IIgs, usually in that order.
By the mid-80s, IBM had firmly dominated the business market and Apple had strong in-roads in schools. While Commodore's earlier 64 could compete due to the low price, the Amiga was not a cheap machine. As a games' machine it was enormously expensive, and most people at this time did not buy a computer mainly to play games, they got a NES for that in the US. The advanced graphics and sound available in the machine was not considered a must-have, whereas PC compatibility was.
While EGA was king, the Amiga and ST ports were usually more than competitive, except for hard drive support. When VGA became mainstream in 1990, the Amiga had no quick answer and with no set hard drive, whatever market the console had in North America vanished.
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