Increased military pressure against Islamic State fighters in both Syria and Iraq led to the group losing 22 percent of its territory in the past 15 months, with about half of the loss coming since the beginning of this year.
That is the result of analysis by monitoring group IHS, which said the militants are "increasingly isolated and being perceived as in decline."
IHS pointed to the area of northern Syria between the Islamic State de facto capital of Raqqa and the Turkish border, where airstrikes from Russia and a U.S.-led coalition combined with Kurdish and Sunni fighters on the ground pushed out the militants and freed key border crossings.
Under IS control
Islamic State now controls only a small portion of Syrian territory where it can smuggle in supplies and fighters from Turkey.
The addition of Russia's bombing campaign was controversial, with Western accusations that its forces were focused too much on targeting rebel fighters in support of Syrian President Bashar al-Assad instead of on Islamic State.
But the start of Russia's airstrikes on September 30 last year marked a significant increase in the overall aerial campaign.
Between January 1, 2015, and the start of Russia's airstrikes, the warplanes in the U.S.-led coalition were carrying out a combined average of 20 airstrikes per day in Iraq and Syria. Since the Russian bombing began, that number has risen to 23 per day, according to a VOA analysis of Pentagon data.
As the collection of forces beat back Islamic State in northern Syria, pro-government forces in Iraq made their own gains, highlighted by the army and Sunni and Shi'ite militias taking back the city of Ramadi.
Iraq plans to make a similar push in the northern city of Mosul, one of the major areas the militants have held for more than a year and a half, but that operation is not imminent.
The international community has pointed to the need for unity in the battle against Islamic State and for the Syrian government and rebels to reach a peace deal in order to allow military resources to focus on eradicating the militants instead.
That process, which saw little progress for several years as more and more people died and millions fled the country, has renewed life with this week's launch of U.N.-led negotiations in Geneva.