One aspects of some modern poets is that they sometimes write sentences without main verbs or no main verb in the main clause. I'm not talking about interjections or sentences where an implied 'be' is unmentioned. I'm talking about sentences like the following:
Song of Myself 42:
Not words of routine this song of mine,
But abruptly to question, to leap beyond yet nearer bring;
This printed and bound book--but the printer and the
printing-office boy?
Or here:
Song of Myself 32:
Myself moving forward then and now and forever,
Gathering and showing more always and with velocity,
Infinite and omnigenous, and the like of these among them,
Not too exclusive toward the reachers of my remembrancers,
Picking out here one that I love, and now go with him on brotherly terms.
Even though each lines ends with a comma, and although the final line does have the verb 'go', 'myself moving forward then and now and forever' is not subordinate to 'now go with him on brotherly terms'. Each line could be thought of as a grammatical unit and does not rely on the other lines for its grammaticality.
Certainly there were poets before Whitman that used unorthodox sentence fragments but it seems to me that Whitman was the first poet to do this on a large scale.