 Complete the following phrase:  Compounding economic difficulties were new military challenges. In the late 1970s, Cambodia under the Khmer Rouge regime started harassing and raiding Vietnamese villages at the common border. To neutralize the threat, PAVN invaded Cambodia in 1978 and overran its capital of Phnom Penh, driving out the incumbent Khmer Rouge regime. In response, as an action to support the pro-Beijing Khmer Rouge regime, China increased its pressure on Vietnam, and 