Nintendo's near monopoly on the home video game market left it with a degree of influence over the industry. Unlike Atari, which never actively courted third-party developers (and even went to court in an attempt to force Activision to cease production of Atari 2600 games), Nintendo had anticipated and encouraged the involvement of third-party software developers; strictly, however, on Nintendo's terms. Some of the Nintendo platform-control measures were adopted by later console manufacturers such as Sega, Sony, and Microsoft, although not as stringent.
Nintendo actively encouraged  the involvement of what?
third-party software developers