This article is the second part of the review of works devoted to the phenomenon of two-stream instability in microwave electronics. As it is known, a problem of creating devices operating in the terahertz frequency range is a rather actual today. Although there are many devices that can generate or amplify signals in this range, most of them refer to extremely powerful relativistic devices. At the same time there is a lack of compact medium power devices. In recent years, models based on the interaction of two electron beams appear in the papers of foreign research groups even more often. This review is an effort more fully describe the articles dealing with such wide in every sense of the phenomenon of two-stream instability in relation to the vacuum microwave electronics. The authors realize that, in general, this phenomenon extends far beyond the boundary of a domain considered here, since this concept is often found in the papers in the field of aerodynamics and hydrodynamics, astrophysics, plasma, solid-state electronics, etc. It follows that the general tendency to shift operating frequencies in the terahertz range gave a second life to two-stream system. Researchers from around the world, especially from China, Korea, Japan, America and other countries, are studying problems related to the generation and amplification of signals based on the two-stream system. In our view, on the one hand, contained in this review articles illustrate fully the interest of foreign researchers in this subject, and on the other hand, are proof of the prospects for further research in this area.