Isberg has served extensively abroad, in Cyprus, Lebanon, Yugoslavia, Macedonia, Bosnia and Herzegovina, Bulgaria, Afghanistan and the Democratic Republic of the Congo.

Isberg is one of only two Swedish officers (the other being Colonel Jonas Wærn) who have served as brigade commanders in combat under the auspices of the United Nations.

[2] Isberg graduated from Military Academy Karlberg (the same class as Ulf Henricsson[3]) in 1969 and was commissioned as an officer the same year in Svea Engineer Regiment with the rank of lieutenant.

[3] Isberg was head of the Army Field Work Department in the Operation Section 4 in the Joint Operations (Operationsledningen, OPL) in the Defence Staff from 1985 to 1988[5][7] and he was promoted to lieutenant colonel in 1986[8] He served as battalion commander from 1988 to 1990, after which he was commander of the Swedish Lebanon Battalions L106/L21 from 1990 to 1991 and commanding officer of the Swedish Army Field Work School (Fältarbetsskolan, FarbS) from 1991 to 1993 and at the same time head of the Swedish UN Stand-by Force in 1992.

The force finally came to include a purely Swedish company instead, now led by major Jan Söderberg.

[10] In January 1993, Isberg was appointed to command Nordbat 1 (Nordic Battalion 1) with the United Nations Protection Forces/Macedonia (UNPROFOR/M), a joint Nordic unit consisting of a mechanized infantry company from Sweden, Norway and Finland, as well as a joint staff and train company from these countries.

[19] In October 2003, Isberg, superseded as brigade commander by a Pakistani brigadier general, returned to his regular position at the MONUC headquarters in Kinshasa, a time as Acting Force Commander; the regular, Mountaga Diallo, was replaced in December by major general Somaila Ilyia from Nigeria, a superior with whom Isberg had easy cooperation.

In mid-March, he led from helicopters and from the ground four major operations aimed at cracking down on the UPC militia's core areas.

The militia quickly opened fire, and in the coming hours, battles were fought over a large area.

[14] At the end of the 2000s, internal and external criticism had been made of the fact that the Swedish Armed Forces did not manage to take care of and implement experience, especially in the context of more complex missions.

Furthermore, an experience management process had already been proposed in the mid-2000s for the then Joint Forces Command (OPIL), but this was considered not to have been fully implemented.