This article provides an insight into how, contrary to popular belief, the presence of firearms created additional reason for unarmed battlefield combat (kumiuchi) and how schools of battlefield combat, such as the Ryōi Shintō-ryū would transition into peacetime Jūjutsu.

From: Takagi-ryū Taijutsu Nitsuite (高木流体術について -About Takagi-ryū Taijutsu)

Yamamoto Yoshiyasu (山本義泰), Undated (possibly 2012-13) - Translated by Logan Weymouth

…during the initial introduction of the firearms, which in no time had widespread visible usage on the battlefield. The battlefield changed forever, due to the distance capabilities of the firearm. In a response to the use of the firearms, there were more instances on the battlefield of soldiers flinging themselves at their enemy to engage in hand-to-hand combat (nikudansen 肉弾戦). 

Here at this point the more original forms of Jūjutsu. were said to have occurred, with the use of the dagger - (kogusoku 小具足) and moving around the hips (koshi no mawari 腰之廻) and their development was remarkable.

Then came the Battle of Sekigahara (circa 1600) and the winter campaign of the Siege of Osaka (1614 CE). During the Genna era (1615-1624), they would enter using the summer battle formations. So, in early modern times (e.g.; 1568-1867) the various parent schools of the ryūha were said to have come into existence.

These were the Oguri ryū (小栗流), Seigō ryū (制剛流), Ryōi Shintō-ryū (良移心当流), Sekiguchi ryū (関口流) were born. These schools were dedicated to preparation for the battlefield i.e. Jujutsu used in armour (katchū jūjutsu 甲冑柔術) andJujutsu used when not in armour (suhada jūjutsu 素肌柔術). It was an imperative to possess both aspects. And after all that came the Kanbun era  (1661). 

The Tokugawa period brought with it comparative peace and the need for wearing armour (katchū 甲冑) had decreased. Thus increasing the opportunity to deliver blows to the vital points of the body (ate waza 当て技 ), which was previously hindered by the wearing of armour. It's believed to have been the cause of the out-branching (of the schools). 

Yori Kumiuchi (armoured grappling) print from: https://za-zen.nl/yoroi-kumi-uchi/