Learn Turkish: Diplomat, taviz vermek yerine ateşkesi bitirmekle tehdit etti. - The diplomat threatened to end the ceasefire instead of making concessions.

The short infinitive structure being taught is used when you tell or want someone ELSE to do an action. Here, the diplomat is threatening to do the action themselves. When the subject does both actions, we use the full infinitive (-mAk). Also, tehdit etmek (to threaten) pairs with the instrumental ending -lA, so bitirmekle literally means 'threatened WITH ending'.

How does yerine work with verbs here?

To say 'instead of doing something', you use the full dictionary form of the verb (-mAk) followed directly by yerine. So taviz vermek (to make a concession) becomes taviz vermek yerine (instead of making a concession).

Why is there an -i at the end of ateşkesi?

It is the specific accusative case marker. The diplomat is threatening to end a specific ceasefire, making it the direct, specific object of the verb bitirmek (to end).

How is the word ateşkes formed?

It is a compound word made of ateş (fire) and kes (the command form of kesmek, to cut). Put them together, and 'cut the fire' becomes the noun for 'ceasefire'.