world-systems
... that in world-system theory, sociologists debate whether two world-systems have ever existed during the same period?
... that in <a class="mw-redirect" href="./World-system_theory" id="mwFBY" rel="mw:WikiLink" title="World-system theory">world-system theory</a>, sociologists debate whether two <b id="mwFBc"><a href="./World-system" id="mwFBg" rel="mw:WikiLink" title="World-system">world-systems</a></b> have ever existed during the same period?