With the exception of the early monophysite and chalcedonian divisions in the first few centuries, and the later schism between Rome and Constantinople, all of which resulted in a separation within the Christian church but no essential change in liturgical practice, the Church remained essentially one in terms of practice until the Reformation.
An important qualifier to this is the understanding that unique liturgical traditions (especially in terms of music forms) were understood to be perfectly acceptable natural developments in liturgical practice, as long as the underlying theology and doctrine remained "orthodox and catholic." Of course, in the medieval period this began to change as subjects like the filioque came to the surface, and the enmity caused by the political and cultural divisions between Rome and Constantinople had more and more impact on the Church.
However, the greatest single change event in the history of Christianity, and certainly in terms of liturgical worship and liturgical music, came with the Protestant Reformation.
Most of these historical and developmental subjects are treated in the various Liturgics sections, and the impact of the Reformation on Protestant Liturgics in this section. "Issues and Questions" is a section that topically addresses specific subjects that are relevant to the subject of liturgical worship and liturgical music in the context of the change that the Protestant Reformation promulgated. It is not a comprehensive or complete offering, but one that offers papers on relevant subjects as they become available.