>>1937>what was done to sabotage the communist party
I can talk about two specific respects in which the movement was externally hindered.
1. Threatening or even SEEKING TO ALTER the existing state structure and institutions, as well as the nebulous ideology that backed the monarchy as symbol and origin of state power, known collectively under the term 'Kokutai', was made a punishable offense of up to ten years hard labor. This was 1925, in the Taisho-jidai, and a cap on the events of the Anarchist-Communist cooperative agitation that had taken place since the 'Freedom and People's Rights' movements of the turn of the century - capping freedom of speech, assembly, and economic redress of grievances. These legal justifications were a post-hoc resolution of what had existed as material policy for many years before, that of violent coercion or defections. The existing structure of the Empire was most definitely aggressive and exploitative (internally and in foreign policy), but the faux anti-imperialist rhetoric, combined with rapid expansions of extralegal force and threat against intellectuals and agitators, led to a precipitous drop in open identification with the party. This certainly muted its effect in the turbulent Taisho democratic era, and the work of notable figures in Marxist economics and other adjacent figures in 'proletarian'-linked social spheres did much to exacerbate the general political campaign against the communists/anarchists.
2. Foreign interference in the party policy and affaires of the early JCP. The clandestine and furtive union of left factions that comprised the early JCP fielded a great wealth of theoretical contribution and debate on the conditions and requirements of socialist agitation in Japan happened to be, unfortunately, contemporaneous to the late 1920's consolidation and unified line of the pre-eminent international organization for communist parties, the Comintern. The demands of the fraternal socialist forces, predominantly the Soviet Union, to exemplify a line of thought that would place prominence on good relations with the CPSU and USSR, rebuke ideas of immediate organization or seizure of state institutions or power, cultivate additional 'right' thought and theory did much to drive a wedge in the party and jeopardize its already threatened legitimacy. The precarious nature of attaining monetary or materiel backing assured that the Koza-ha (Soviet backed faction, 'lecture' is its name) would predominate over any opposition group and could effectively control party politics. The expelled or disillusioned persons of the opposition faction Rono-ha (labor-farmer) were marginalized, purged, or left the party. This was primarily over a simple distinction of what form of capitalist property relations constituted the Japanese Empire at that time. The JCP, under Koza-ha, continued to suffer reprisals by the Tokkō, a special police auxiliary, but emerged from the war as perceived vindicated by the general malaise with war and militarism. Unfortunately, the Korean War came and further demands placed on the party by the Soviet Union and China to actively disrupt the American war effort by sabotage had failed to account for the atrophy of previous policy in the party. Already suspect by American occupation authorities, despite professed legality, the JCP would suffer schism and debilitating loss of confidence in its lack of independent program and reliance only on the legitimacy of Empire-era dissident status. This gradual effacement plagues the party even today, as the party does little meaningful work beyond cursory education.
Sorry that took very long to write. The party does good work, too, but times are bleak.