Islam was spread by the sword? What about Christianity?

The Pope has got in hot water for quoting an obscure Byzantine emperor
Manuel Paleologos II who once said: "Show me just what Muhammad brought
that was new, and there you will find things only evil and inhuman,
such as his command to spread by the sword the faith he preached."

Wasn't Christianity spread by the sword? I am thinking of the Crusades,
the Conquistadors, the Roman Empire enforcing Christianity as the sole
religion of Europe. Other examples are the crushing of Native Americans
to make North America a Christian land (Protestant), and bringing
Christianity to the new colonies of Africa in the 19th Century.
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