In 1962 and 1963, three papers were written incorporating international trade into the IS-LM model. The development of the model is recounted by Nobel Laureate Robert Mundell here. This model was the workhorse for Keynesian open economy macro for an academic generation, and we'll go over it in the lecture. The lecture is a stripped down version of this talk.
Here's a handout of the slides and the slides themselves are on slideshare.