The Assyrian is addressed. That spoilest, etc.] may mean, (1) that the Assyrian attacked Judah without provocation, or (2) that he has so far spoiled other nations unchecked.
Related Commentaries of Isaiah 33:1
Isaiah 33:1
1 Woe to thee that spoilest, and thou wast not spoiled; and dealest treacherously, and they dealt not treacherously with thee! when thou shalt cease to spoil, thou shalt be spoiled; and when thou shalt make an end to deal treacherously, they shall deal treacherously with thee.