"became decisive" is a correct and usable phrase in written English.
It can be used to describe a moment or action that had a significant impact or determined the outcome of a situation. Example: "After months of debate and deliberation, the leader's sudden change of heart became decisive in the final decision."
I tapped into fresh reserves of creative energy and became decisive.
The art of maneuver became decisive, and analysis of war was couched accordingly in terms of strategies.
At the other extreme were the arrangements made in British Columbia, which became decisive when it entered the Canadian Confederation, to establish and maintain a free, unified, centralized nonsectarian system.
Hence their accustomed advantage vis-à-vis infantrymen was undermined when gunfire became decisive on the battlefield, as it did throughout Eurasia by the beginning of the 18th century.
These quantities are quite sensitive to the form of the decay interaction and became decisive pieces of evidence in the search for the form of the decay interaction.
Zhu's influence rose at the end of the Southern Song dynasty and became decisive during the Yuan dynasty when his edition of the Four Books was adopted as the basis of the imperial examination system arranged by scholars trained in his approach.
As responsibility is devolved, the firm should become decisive and agile.
In particular, constraints to grazing become decisive in a zero-deforestation world.
When using high strength steels for pressure vessels, cyclic fatigue requirements may become decisive for the design.
The amount of mineral admixture becomes decisive for the variations of impedance spectra, model parameter and carbonation depth.
Capablanca perfected the skill that players call technique, the nurturing of tiny advantages until they become decisive.
