Joined by the five domains in Echigo such as the Shibata Domain and the Echigo-Nagaoka Domain when negotiations with the new government's forces collapsed because armed neutrality was rejected, an alliance was established by a total of thirty-one domains.
同盟には、武装中立が認められず新政府軍との会談に決裂した越後長岡藩、ほか新発田藩等の越後5藩が加入し、計31藩によって同盟が成立した。