Comparison of Systems

Does anyone have a top-level comparison of the various systems.  A table may serve, followed by more detailed explanation of the differences ... followed perhaps on a historical perspective on the behind-the-scenes machinations.  There was an idea once upon a time that there would be a universal (global) HDTV standard ... does anyone have a good handle of how this patchwork quilt emerged from the good intent to agree on a global HDTV system?