What happened with the recent failed G7 summit is an escalation of a process that began with George W. Bush’s lying his way into a war of choice in Iraq: a series of real-life examples of why it is undesirable to have a sole global superpower in the world. As we are seeing, that superpower might just run off the rails, as countries tend to sometimes do.
It is not necessary to have any deeper understanding of how the machinations of capitalist class society make this inevitable; the lesson can be learnt, in incomplete form, whether or not one is a leftist who inquires into the nature and implications of class society. It is broader than capitalism, anyhow: regardless of the socioeconomic system, any gross disparity of power is fated to eventually prove itself to be the danger that it always was.
It was possible for students (i.e. those in other nations) to dismiss the first lesson as a historical anomaly when Obama won office. It will not be so easy for them to wave off the second, ongoing one.
The US Empire has inflicted a mortal wound upon itself. The wound may not initially appear to be mortal, but in time it will prove to be. It will not go away when Donald Trump goes away. It may even sometimes appear to be healing and the patient on the way to recovery, but such episodes will prove to be false hopes on the part of those making them.
The US empire is not ending in the way most of us on the left hoped it would, but it ending it is.