史上空前
shi.jou.kuu.zen
Literally: history – above/up – empty – before
Alternately: Unprecedented. Unheard of. History-making. The very first ever.
Notes:In cases like this, the 上 character refers to a vague scope of the topic under discussion. It can also be read as “from the point of view of ~.”

A serious example for once – my usual image search turned up this picture of an article about the Arab Spring.
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