When did Finland and Sweden join NATO?
Russia's invasion of Ukraine prompted Finland and Sweden to apply for NATO membership in May 2022, and the ratification process for Sweden is in progress. Finland officially joined on 4 April 2023. Ukraine applied for NATO membership in September 2022 after Russia claimed to annex part of its territory. Two other states have formally informed NATO of their membership aspirations: Bosnia and Herzegovina and Georgia. Kosovo also aspires to join NATO. Joining the alliance is a debate topic in several other European countries outside the alliance, including Austria, Ireland, Malta, Moldova, and Serbia.
Finland officially joined NATO on 4 April 2023, while the ratification process for Sweden is in progress.
Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.
### Instruction: When did Finland and Sweden join NATO?
### Input: Russia's invasion of Ukraine prompted Finland and Sweden to apply for NATO membership in May 2022, and the ratification process for Sweden is in progress. Finland officially joined on 4 April 2023. Ukraine applied for NATO membership in September 2022 after Russia claimed to annex part of its territory. Two other states have formally informed NATO of their membership aspirations: Bosnia and Herzegovina and Georgia. Kosovo also aspires to join NATO. Joining the alliance is a debate topic in several other European countries outside the alliance, including Austria, Ireland, Malta, Moldova, and Serbia.
### Response: Finland officially joined NATO on 4 April 2023, while the ratification process for Sweden is in progress.