The Great Abjuration was a massive shift in trends regarding military application of magic during the Second Ettish War, where evocation magic fell out of favor in large-scale formation fighting and whose status of battlefield primacy was ultimately replaced with abjuration and illusion magic.
The previous dominance of Evocation magic largely came as a result of existing philosophy mandating that magical potential should be utilized to deal the greatest amount of tangible damage to an opposing force as humanly possible. However, as time went on, armies with weaker magical capabilities developed stratagems to oppose this status quo. In particular, the asymmetrical warfare practiced by the Republic of Ettmark and Black Army of Wudor mitigated the effect of spells that affected a large area, as spellcasters often had little time to prepare powerful spells before the start of battle, while opposing formations were not as tightly clumped. Lower-level magickers looked towards spells such as Silence and Counterspell to interrupt the casting of high-level mages’ casts, and utilizing these spells to deny the enemy destructive potential (specifically the usage of silence to interrupt a large number of casters simultaneously) allowed smaller magical contingents to outmaneuver larger ones, and allowed magic users of lesser proficiency to stand their ground against those with higher amounts of raw magical output.
This period introduced the concept of a “Mana Skirmish,” in which magicians on either side of an opposing force would attempt to bait out powerful and demanding spells in order to use a less mana-intensive counterspell to either avoid damage or mitigate the effect, thus providing an advantage to the “winner” of the Mana Skirmish. Similarly, mages could utilize minor illusion or willingly mis-speak verbal components of powerful spells to set up a ruse of casting a powerful spell, baiting their opponent into utilizing mana to cast silence, counterspell, or some sort of protective incantation.
The fallout of purely evocation-conjuration magical contingents in standardized armies spread to both the Evershining Empire and the Teurechti People fiefdoms to the west, favoring a style of military applications of magic that isolated and confused enemies while denying the opposing group as much destructive value out of their mages as humanly possible.
The transitional period between First Shining Empire era evocation tactics and the Great Abjuration led to a long period in which magic’s practical use in mass combat vastly decreased, such as naval battles in the Velmiric Slave Raids in which both sides brought a shipborne contingent of mages who were there only to cast Counterspell.