Have You seen system requirements of Civilization 5?
CPU: Intel Core 2 Duo 1.8 GHz or AMD Athlon X2 64 2.0 GHz
CPU Speed: Intel Core 2 Duo 1.8 GHz or AMD Athlon X2 64 2.0 GHz
RAM: 2 GB
OS: Windows XP SP3/ Windows Vista SP2/ Windows 7
Video Card: 256 MB ATI Radeon HD 2600 XT or better, 256 MB NVIDIA GeForce 7900 GS or better, or Core i3 or better integrated graphics
DirectX version: DirectX® 9.0c
Sound Card: Yes
Free Disk Space: 8 GB Free
It can be practically ran by mediocre android cellphone [figuratively spoken]. If You give me a budget, I'll pick You a notebook. And also screen size.