Countries with a history of successfully removing the right to bear and own firearms, how was it possible? I'm more curious about
I can answer this for Sweden, at least.
Swedish medieval county laws required the peasants to own, keep and train with arms and armour and serve in the Ledung, the war fleet, if called by the King or pay taxes for someone to go in their stead. This was replaced in 1280 with the Alnsö law that gave worldly tax exemption to those that could provide an armoured rider (ie a knight) for the King's service. However, Swedish peasants continued to keep, own and train with arms long after this, and were by the end of the Kalmar Union in 1521 experienced, well trained and well armed and armoured, partially from looting the battlefields in the victories in the long civil war/clusterfuck that was the Kalmar Union.
King Erik XIV considered purchasing arms and armour from the peasants to equip new formations to replace losses during the Nordic Seven Years' War 1563-70, but reports indicated that the arms and armour the peasants still kept were obselete and often in bad shape from age and lack of maintenance, and the plan was scrapped. But the fact that the plan was considered at all indicates that the peasants were still in posession of large quantities of arms and armour.
The Swedish self-owning peasants usually owned between 33 and 52% of the arable soil in Sweden (rising to 90% in the end of the 19th century) and could afford to keep arms. However, after the 1600s, their share of the population started to decline as a new class of crofters, proto-industrial workers, day labourers, farmhands and other lower class individuals arose under them. It is important to note that this class rarely if ever could afford to buy weapons, especially as weapons became more advanced and expensive. Thus regulation of arms ownership was an issue that did not affect a large percentage of the populaton, because they were too poor to own arms anyway.
The first law regarding ownership of firearms came 1927. Before that, anyone could own any arms they liked. The process to gain a permit was rather easy - owning any agricultural or forested land (or being part of a family whose head owned land) was enough to get a hunter's license for rifles and shotguns. Feeling a need for protection was enough reason to get a license for pistols and revolvers. The matter was a formality, walk to the police station, register for a license and then purchase a weapon over the desk at a store selling arms. The license requirements were mostly introduced as a rather late response to the fear for revolutionary activity. The authorities feared various left-wing radicals "running around with a revolver in their pocket" and the law gave the police the ability to arrest people that carried arms without license.
1934, the requirements were increased, partially as a response to the right-wing "Munckska Kåren" white guard that were established 1927 by conservatives fearing a communist take-over and arming themselves (with the permission of the police) with 40 SMGs and 300 pistols with 10 000 shots purchased from Germany. When the organisation was discovered in 1931, an uproar in the newspapers caused the authorities to force the organisation to deliver their then around 1 500 guns to the police.
The 1934 law also required all existing owners of arms to register them with the police, which had not been a requirement in 1927.
From 1934 onwards, "specific reasons" were required to get a license for handguns. What "specific reasons" are have changed over time. The need for self-protection is no longer a valid "specific reason" and you need to be an active sports shooter that competes regularly and shoots above a certain level to get a license for a .22 handgun today. Once you have been active with that weapon for some time, you can get licenses for heavier calibre handguns.
Rifles and shotguns are still handled through a hunter's license, where you need to go through a hunter's training to get a license. Hunting was and is an important pastime in Sweden, and the hunters' associations are influential when it comes to weapon laws (which is why it is much easier to get and above all keep a license for a rifle than for a handgun).
The laws were changed to add more restrictions in 1949, 1973 and 1996.
However, there were also many other arms. The Swedish Hemvärn (Home Guard) was formed in 1940 and every man equipped with a military weapon, which was stored at the Home Guardsman's home together with ammunition. Police, postal workers, bank employees and some other were armed by their employers and expected to keep weapons at home or on their person when at their workplace.
Military arms were also stored in decentralised locked strongboxes and small safehouses in the countryside to allow a decentralised mobilisation to take place should Sweden be attacked in coup-like circumstances after ww2. After repeated break-ins and theft from these storages by criminal elements in the 1990s, the system was de-established.
How was this handled? Old licenses remained even as laws changed, but new ones were not issued, often forcing children of gunowners to sell or turn over weapons to the authorities for destruction once the owner died. The only time the authorities forced a large turnover of arms was when Munckska kåren was forced to turn over 1 500 weapons 1931-32, but those were owned by the organisation and not by the individual members, even if some were stored at the homes of individual members.
The regulation of arms were a non-issue to most people, as most people did not own weapons, and hunting arms have continued to be relatively easy to acquire and keep. There's roughly 2 million weapons in Sweden, to about 10 million people. One of the most armed counties is Jämtland, where there's roughly 60 000 weapons to 100 000 inhabitants.
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A follow up question based on his question:
What countries actually have removed the right to bear and own firearms? As far as I know, in all european countries you can own firearms.