During the Estonian War of Independence, Tief was a commander in the Kalevlaste Maleva battalion formed in 1918 by members of the Kalev sports society.

Tief then published a proclamation, re-establishing the independence of the Republic of Estonia on the basis of legal continuity, and attempted to organise the defence of Tallinn against the invading Red Army, which pushed into the capital on 22 September 1944.

After being able to return briefly to Soviet-occupied Estonia in 1955, Tief was again forced to live in exile in Soviet Ukraine until 1965, when he was permitted to relocate closer to home, and he could then reside just on the other side of the Estonian border in Latvia.

[5][6] Although the attempt to restore Estonian independence in September 1944 did not succeed, the Tief government proved to be an integral and indispensable part of the de jure continuity of the Republic of Estonia.

In February 2007 the Estonian parliament decided to commemorate the actions of Tief's government by proclaiming 22 September the annual "Day of Resistance".