The phrase "a decisive step in" is correct and commonly used in written English.
It is typically used to indicate that something is an important or crucial part of a process or journey. Example: "The signing of the peace treaty was a decisive step in ending the long-standing conflict between the two nations."
The Sherpa rights group hailed the decision to charge the company, saying it was "a decisive step in the fight against the impunity of multinationals operating in armed conflict zones".
It was a decisive step in the breakup of the Maratha confederacy.
It also takes a decisive step in changing how insurance companies deal with the costs of health care.
Representative Lincoln Diaz-Balart, Republican of Florida, called it "a decisive step in the weakening of the United States".
The Greek and Turkish governments took a decisive step in February 1959, when they reached an agreement in Zürich.
He views the little painting as a decisive step in the evolution of Duccio's style, which reached its apogee about eight years later in the "Maestà" altarpiece.
With a common European currency, Europe has taken a further decisive step in integration.
The Bank of England has taken a decisive step to restore confidence in the banking system.The "special liquidity scheme" launched this week puts Britain's central bank at the forefront of international attempts to arrest the financial crisis.
Though number to the early Pythagoreans was still a kind of cosmic matter, like the water or air proposed by the Ionians, their stress upon numerical proportions, harmony, and order constituted a decisive step toward a metaphysic in which form is the basic reality.
While still a natural philosopher, she has taken a decisive step toward modern science in her masterwork, Foundations of Physics.
Cooperation between the EU and ESA in the development of Galileo marked a first decisive step in collaboration between these two communities.
