The Federated Malay States was a federation of four states
on the Malay Peninsula - Pahang, Perak, Selangor, and Negri Sembilan - established
by the British government in 1895, and lasted until 1946, when they were joined
to the Straits Settlements and the Unfederated Malay States in the Malayan Union,
then Federation of Malaya and later Malaysia.
The United Kingdom was responsible for foreign affairs and defense, whilst the states continued to be responsible for their domestic policies. Even so, the British Resident General would give advice on domestic issues, and the states were bound by treaty to follow that advice.
While the four states issued their own postage stamps as before, there were additional issues for the Federated States as a whole:
In 1935, the federation issues were replaced by those of the individual states, but federation still continued issuing postage due stamps which were valid in all states until the establishment of the Federation of Malaya.