The most common and most likely answer to this crossword clue is the 9 letter word PRESSURES
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More clues leading to the result PRESSURES
Buddy explains!

The straight part
We know that "forces" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case forces = pressures.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PRESSURES mean?
PRESSURES noun- A pressing; a force applied to a surface.
- A contrasting force or impulse of any kind
- Distress.
- Urgency
- Impression; stamp; character impressed.
- The amount of force that is applied over a given area divided by the size of this area.
- To encourage or heavily exert force or influence.