As warfighting technologies have developed and access to effective medical care has improved, the incidents of Traumatic Brain Injuries (TBI's) has for those serving in military operations.

The missing word is Increased.

Explanation:

As warfighting technologies have developed and access to effective medical care has improved, the incidents of Traumatic Brain Injuries (TBI's) has increased for those serving in military operations. This increase is partly due to the prevalence of Improvised Explosive Devices in warfare by the enemy.

TBIs can range from mild, to moderate, and severe.

Some of it's symptoms include but are not limited to:

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