The stack property in the Kendo Area Chart does not honor groups as separate stacking contexts.

Instead, everything gets stacked together if `stack: true` is applied.

For other chart types you can overcome this instead of just stack: true, set different stack groups, such as "A" and "B", so they do not stack together.

series: [

    {

     field: "value",

     categoryField: "year",

     name: "United States Group 1 - Series 1",

     stack: "A",  // Separate stack group

     opacity: 0.5  // Transparency for visibility

    },

    {

     field: "value1",

     categoryField: "year",

     name: "United States Group 1 - Series 2",

     stack: "A"   // Part of the same stack as the first one

    },

    {

     field: "value2",

     categoryField: "year",

     name: "United States Group 2 - Series 1",

     stack: "B"   // A different stack group

    },

    {

     field: "value3",

     categoryField: "year",

     name: "United States Group 2 - Series 2",

     stack: "B"   // Part of the second group stack

    }

]