Liechtenstein is the only European nation that still has

[ParthJ26]

6th Edition FoV Pg 116.

Liechtenstein is the only European nation that still has a monarchy with real - rather than largely ceremonial or diplomatic - power, and where the power given to the sovereign has actually increased in the current millennium.

Dear Team,

Hi.

And = parallelism marker.

So after And, we have

where the power is given to the sovereign has actually increased in the current millennium.

Before And, we have,

that still has a monarchy with real-rather than largely ceremonial or diplomatic - power

Why is it incorrect to compare a phrase that starts with THAT to a phrase that starts with where, when, which, who?

Thank you.

Best,
Parth.

[Sage Pearce-Higgins]

Because the two phrases aren't parallel. You can either simply memorize this, or you can keep in mind that we're always asked to compare sentences in SC, so that, disregarding other potential issues, a sentence that is more parallel is more desirable.