From an earlier answer of mine

Although they were separated by an entire globe, different geopolitical contexts, and massively different political cultures, there were a surprising number of overlaps and parallels in both Japanese and West German rearmament in the 1950s. Creating armed forces, who were initially composed of veterans from the Second World War, was a tricky proposition that had to both navigate domestic opposition and international leeriness of rearmed Axis powers.

In both cases, rearmament was largely enabled by postwar political actors that not only saw a military as a defense against potential Soviet aggression, but also as a means to regain national sovereignty. Although their US superpower patron certainly facilitated this position, especially by encouraging the type of anticommunist politicians like Konrad Adenauer or Yoshida Shigeru to come to the forefront of postwar politics, rearmament was almost a geopolitical given among a certain subset of postwar politicians. Allied military government was anathema to various politicians and the emerging Cold War underscored both the need to rearm, but also frame it within the nascent aegis of an American-led military coalition. Therefore, rearmament ticked off two important boxes that legitimized the postwar leadership of Japan and Germany: not only did armed forces signify independence, but their integration into these networks normalized the process of rearmament.

In both cases, rearmament faced a difficult battle with the postwar constitutions and other legal muzzles. Although German Basic Law did not go to the extent of Japan's Article 9 in its antimilitary provisions, Basic Law posed a set of problems to Adenauer and his rearmament team within Amt Blank. Part of the problem was that the legal position of a future military was absent within the original constitution. This left a proto-German military in a legal null zone, as there were no real provisions to where it stood legally. Article 26 outlawed aggressive war and Article 4 enshrined conscientious objection, but that was about it. In the domestic debates about rearmament, opponents of rearmament in the SPD used both Articles 4 and 26, as well as Basic Law's ambiguity about military matters, to argue that reforging the military was against the spirit of the constitution. Ob the flipside, proponents of rearmament in the CDU/CSU and political center pointed out that Article 4 denuded rearmament of its coercive character and Basic Law's provisions for recognition of international authority were significant safeguards against a rebirth of German militarism.

Article 9 in Japan was far more stringent in its antimilitarism than Article 26, but it too had ambiguities that pro-rearmament politicians could exploit. Much like the Allied Control Council's declaration abolishing Prussia, Article 9 was born out of an idea that certain national characteristics were innate, in this case militarism, and the occupation had to radically restructure society to break these entrenched attitudes. As head of SCAP, MacArthur alternated between a condescending, somewhat racist view of the Japanese, and a real zeal to radically reform Japan along American lines. MacArthur's quasi-imperial governance of SCAP/GHQ meant that major initiatives could emanate from below and receive the blessing of SCAP's powerful head. Given SCAP's somewhat eclectic staff, which ranged from fervent anticommunist right-wingers to New Dealers, this imparted a somewhat incoherent occupation policy. The renunciation of war was likely the brainchild of Colonel Charles Kades, a New Dealer and chief aide of General Courtney Whitney, who was greatly influenced by the symbolic power of the Kellogg-Briand pact. Both Whitney and Kades outlined the future (non)status of the Japanese military in a January 1946 meeting with Prime Minister Shidehara that the constitution would outlaw war. The initial SCAP/GHQ proposals were even more stringent, going so far as to suggest that Japan did not even have the right to self-defense. As with a number of SCAP diktats, this extreme position engendered a certain resistance among Japanese lawmakers, but they recognized, much as Adenauer and his cohort, that they had to work within the system of Allied occupation. Asida Hitoshi, an influential member of the Diet's subcommittee on constitutional revision, proposed an amendment to SCAP/GHQ's constitution that softened the language by outlawing war as a means to settle international disputes. This was became the constitutional loophole from which the Self-Defense Forces (SDF) emerged, and MacArthur, with the Cold War looming on the horizon, approved of this softening of Article 9.

Although the rearmament cliques in both Japan and Germany triumphed over their constitutional opponents, they faced a deeper struggle against domestic opinion that had a strong streak of antimilitarism that defeat had enabled. In Germany, the ohne mich (without me) was an extremely strong sentiment over conscription and the issue of who exactly Article 4 applied to was a very contentious issue. Part of the reason why West Berlin became something of a radical hotbed for the West German left in the 1960s was not only the legacy of "Red Berlin" as a stronghold of the SPD, but also because conscription did not apply to its residents. Prominent German public intellectuals like Eugen Kogon weighed in on rearmament as a disturbing development, either as the least-worst alternative to communist domination or as a sign of a larger reneging on postwar promises to fundamentally recast German society and culture. The public attitude to the military was arguably colder in Japan than in Germany. The memory of militarist rule ran long in Japan, and unlike Germany, it was much more difficult in Japan to disentangle the public image of the military from the regime it served. Therefore, the antiwar provisions in Article 9 became something of political litmus test in Japanese politics, with some embracing its ideals, and other politicians lightly decrying it as a straitjacket on Japan. Shidehara claimed authorship of Article 9, something that both Whitney and Kades denied, and the ideals of the "Peace Constitution" became an entrenched facet of Japanese politics. On the other end of the scale, Asida claimed his rewording of Article 9 paved the way for the SDF, something that declassified minutes of the committee do not reveal.

What transformed rearmament from a contentious hypothetical into a reality was the Korean War. Yoshida Shigeru would refer to the Korean invasion as "a gift from the gods" as the immediate need for Japanese bases gave the conservative government a chance to structure the SDF along the lines it wanted. The economic boom caused by the war helped stabilize Japan, but also overshadowed Yoshida's camouflaged rearmament. But not all politicians shared Yoshida's positive assessment of Korean developments. Although the actual performance of the US military against the DPRK and later Chinese volunteers looked better in retrospect, from the perspective of 1950 it looked quite different. Within the Western European press, the Korean invasion stoked a significant war scare, especially in the FRG which drew parallels between the DPRK's rhetoric about a united Korea and the SED's call for a unified Germany and the formation of the SED's own militarized police force. In 1949, Western defense planners estimated that it would take 54 divisions to use the FRG as a glacis against a Soviet invasion, and the three Western armies could only muster 10 divisions in 1950. Te war also sparked concerns that the US, despite its avowed public commitment to anticommunism, would wither under the chastening of Korea and return back into isolationism.

These fears helped to break the Western European loggerheads against German rearmament. While German public opinion on rearmament was decidedly mixed, the Western European opinion on a rearmed Germany was more unequivocally negative. Not only was public opinion against it, but there was a strong distaste for German rearmament among key policymakers as well. The British Foreign Office wished only for a limited rearmament and even toyed with the idea of a federal German army composed of separate Land armies, a throwback to the nineteenth century. In France, Prime Minster Pleven proposed a scheme of a pan-European army, which would later morph into the European Defense Community (EDC). The German contingent to the EDC would be under European control and strictly limited in numbers and personnel (the EDC would not allow German conscription). Meanwhile, Bonn used the EDC to make the plans of Amt Blank into a reality and there was considerable friction over both force structure and limits between the FRG and Western Europe with the Germans treating the maximum allowable German EDC force as the acceptable minimum. Not surprisingly, the EDC fell apart from having too many cooks and the overall unpopularity of German rearmament. The French parliament's refusal to ratify the EDC ended this attempt at a European military. Ironically, proponents of rejecting the EDC framed its rejection as a move that would prevent German rearmament when it actually did the opposite. US sponsorship of the EDC, done partly out of concerns created by Korea, laid the groundwork for provisioning a German military with equipment and the EDC negotiations forced the Adenauer government to think seriously about the scale of a German army and its position within the political system.