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The first generations of astrophysical objects made a substantial impact onour Universe with their radiation. X-rays from the first sources, with largemean free paths, likely quickly heated the intergalactic medium (IGM). Thesecond generation of 21cm instruments can provide a unique view into this earlyepoch. The early stages of reionization likely followed, driven by so-called"minihalos", i.e. molecularly-cooled halos. These small halos were susceptibleto complex feedback mechanisms, especially from the soft-UV background whichpreceded reionization, resulting in complex and possibly extended early stagesof reionization. When atomically-cooled galaxies emerged as the dominantionizers, reionization could proceed more rapidly, with these being lesssensitive to radiative feedback than previously thought. Reionization couldhave slowed in the final stages when the ionized bubbles grew larger than theseparation of Lyman limit absorption systems (LLSs). The final stages likelyinvolved the photo-evaporation of LLSs, which by then regulated the rise of theUV background. I discuss the theoretical underpinnings of this narrative, aswell as how future 21cm observations may help shed light on the outstandinguncertainties.

How the first generations of luminous baryons established the X-ray and UV backgrounds