The scale and ambition of nationwide interconnected greenways and trails merits their recognition as a distinctive stage of third generation (G3) greenways, referred to here as G3+.• Lessons learned from the experience of developing nationwide greenways, such as the Trans CanadaTrail and the Sendero de Chile, have received limited scholarly attention to date. • A model of a virtuous cycle brings attention to the reliance of large-scale greenways development on the positive feedback between political and public support for the network connectivity.A new generation of greenways has emerged in recent years, the most ambitious of which are nationwide, interconnected networks of multi-use, multi-purpose greenways and trails, clustered under a single national vision. However, because these initiatives have been the focus of so few research studies, opportunities to glean lessons from their planning and implementation have been limited. This paper contributes to addressing this knowledge gap by presenting a comparative account of two networks, the Trans Canada Trail in Canada and Sendero de Chile in Chile. Using document analysis and interviews with officials closely involved in their development, the evolution of both networks is documented over time, emphasizing similarities and differences related to their planning and implementation. Both initiatives have faced significant challenges in reaching their connection goals and have availed themselves of a diverse range of opportunities and strategies to advance their agendas. A simple model of a virtuous cycle is proposed to highlight the positive feedback-between political and public support, sustained funding, partnership development, accessibility for urban residents, and connectivity of the network-generated by sustained network expansion over time. It is hoped that the insights offered from this analysis may offer guidance to inform the development of similar scale projects elsewhere.