Side's

A frosty east-west relationship led to a sort of brinkmanship where both NATO and Russia flew military aircraft close to the other side's frontiers or even deliberately made brief incursions into the other side's airspace, either to test air defence capabilities or as part of a pattern of intimidation or coercion.

I bought a scarf for my grandfather on my father's side's 88th birthday.

You don't even know the other side's arguments, so of course you're going to misinterpret everything they do.