The phrase 'ruthless world' is correct and can be used in written English.
You can use it to describe a situation that is chaotic or unkind, and often without mercy. For example: "In this ruthless world, it's every man for himself."
"It can be a nasty, ruthless world.
It's a ruthless world out there.
You become accustomed to what a ruthless world it is out there".
Ms. Kirchschlager, at 33, has risen rapidly in the often ruthless world of operatic singing.
For all his struggles at Barcelona, this is a genuinely fine, delicately ruthless world star.
How can we be true to ourselves and survive in a ruthless world?
She now has to deliver this case to a Mr. Jan, a brutal syndicate-head, impeccably played by a perfectly-cast Min-sik Choi, who inscrutably maintains the ruthless, world-weary countenance of an always-calculating villain, and, who in one scene washes blood from his hands with an Evian bottle, the red letters of which match the blood, making for an odd (unintentional?) product placement.
Scott was more popular in the ruthless corporate world of the 1980s, while Shackleton is more the man for today.
When the only real goal of an operation is to keep a deep-pocketed corporation happy, it's hard to find any principles to latch on to, and holding on to battered ideals and personal loyalties is a real liability in this ruthless, cynical world.
But behind the glib promises and the slick online communications is a ruthless real-world web of smugglers and con men who thrive on the vulnerability of the migrants.
The Nazi military machine was the most ruthless force the world has ever seen.
