Why go back to the delta wing again?
The delta planform, despite it´s disadvantages, still has a lot going for it. The wing has a long root (chord) and this allows the root to be fairly thick for a given drag coeffecient. This,in turn, allows for a considerable increase in internal volume which can be used for fuel or avionics. Also, the delta provides a considerable wing area for a given wingspan and for a given weight it is also a very strong structure. The introduction of FBW technology and relaxed stability allowed Dassault to take advantage the delta planform´s undeniable strong points whilst eliminating or at least minimising the weaknesses, such as a low sustained turn rate. The high usable volume is evident when comparing the internal fuel capacity of the single seat version with that of the two seater. The two seater B or D lose only some 80 liters of fuel. By contrast a F18 D Hornet loses some 350 litres and the F16 D loses about 800 litres. This is the result of the Mirage 2000 carrying a higher proportion of it´s fuel in the wings. Hence, only a small amount of fuel capacity is sacrificed when a second seat is added.

 Relaxed Stability
Dassault did this by designing the Mirage 2000 in such a way that the centre of gravity is positioned well behind the centre of lift. This means that the aircraft is positively unstable in pitch ie. the nose wants to pitch upward all the time. The wings also have leading edge flaps. These flaps move downward thereby increasing the camber (curvature) which generates more lift. The leading edge flaps are controlled by the analog Flight Control System (FCS) and deployed when the aircraft is engaged in a manouvring flight profile such as a dogfight. The Mirage 2000 FCS Law is based on G Factor limited by Angle of Attack(AoA) which is 29° in clean configuration.
A further benefit of the computer controlled FCS is the automatic G-limiting. Previous generations of fighter aircraft required the pilot to constantly monitor his position within the flight envelope so as to avoid damaging the aircraft. During aircombat a pilot has enough on his mind without having to worry about the limitations of the airframe and wings. The FCS constantly monitors the weight of the plane and associated flight parametres and prevents the pilot from overstressing the airframe. Dassault have programmed the FCS of the Mirage 2000 to allow 9G manouvring and a roll rate of 270°/sec when configured for air-to-air combat although the pilot can pull an extra 30kg rearward force on the joystick to allow an extra 2G for a total of 11G. When the aircraft is loaded for an air-to-ground mission the FCS limits the aircraft to 5.5G and 150°/sec roll rate and the application of 30kg force on the joystick increases the G-limit to 7.5. At low speed the FCS is switched to Alpha-demand. At approximately 245 Kts the FCS transitions to G_Demand..
The FCS was developed by Dassault without any outside involvement. Indeed, Dassault believe that the FCS is the single most important factor influencing a pilot´s opinion of an aircraft and as such never let anybody else develop it for them.
  A visible manifestation of the FBW system is the frantic movement of the elevators when a FBW-equipped aircraft taxies along the runway or apron.